Publications

We present a three-terminal resistive switching device with a 20 mol% gadolinium-doped ceria (20GDC) thin film as the solid state electrolyte. The device features a top Ta-metal gate electrode and bottom Ta-metal source and drain electrodes, separated by a 1 mm gap filled with 20GDC. Its operation relies on the redox reaction of cerium, specifically the reduction of cerium (IV) to cerium (III) at the interface between the Ta-gate and the 20GDC electrolyte. Under positive gate bias, the Ta gate electrode undergoes oxidation, while cerium is reduced, forming a conductive layer between the source and drain electrodes. Applying a negative gate bias reverses this effect. To confirm that resistivity changes originate from interface redox reactions, we conducted cyclic voltammetry at 403 K. The results demonstrate that peak current is inversely proportional to the scan rate, a characteristic of reaction at a surface. Additionally, we demonstrated that sputtering a TaO_x blocking layer beneath the gate electrode suppresses resistive switching. While the resistance changes only by a factor of two, the proposed device operates near equilibrium, is simple to fabricate, and exhibits high robustness. These characteristics make the concept of interface oxidation/reduction appealing for further exploration.

Non-classical electromechanical properties, such as large electrostriction stress coefficient and low dielectric constant in Zr-doped ceria and other doped cerium oxides, discovered in the last several years, are the focus of intense research as they indicate the existence of solids with unusually large anharmonicity of chemical bonds. Theoretical models of electrostriction mechanisms rely on the concept of elastic dipoles that are formed due to the local structural distortions around dopants. The structural, dynamic, and electronic descriptors of the pre-existing (at zero field) dipoles (as in aliovalent-doped ceria) and those dynamically formed under the electric field (as in isovalent-doped ceria) are unknown. Here, the characteristics of the local structure and dynamics of the dopant and host bonding environments were obtained by using the temperature-dependent X-ray absorption fine structure measurements. The candidate set of descriptors was identified in a quasiharmonic approximation for the nearest neighboring bonds between Zr (Ce) and the atoms in the first and second coordination shells. The descriptors included static bond length disorder, the anharmonicity of the effective pair potential, and effective force constants for the probed atomic pairs. The observation of significant Zr-O bond anharmonicity confirms previous first-principles calculations. The structural model, emerging from these simulations, emphasizes significant free volume around Zr in the oxygen cube, explaining both the mechanical anomaly (the decrease in Youngs modulus with Zr concentration) as well as correlating at least one descriptor (static disorder) to the measured electrostriction coefficient. This descriptor-based approach can be extended to studies under applied electric fields or stress in this and other materials.

In search of different chemical mechanisms for electro-freezing of supercooled water (SCW), we describe here the differences between the inert electrodes of Co and Ni and their ability to be converted into ice makers. The formation of crystalline domains by anodic electrochemical treatment of cobalt in 10 μM KOH solution triggers ice nucleation of supercooled water at ∼−3 °C without the application of voltage. X-ray diffraction and XPS demonstrate that these crystalline domains are composed of oxyhydroxide molecules. As predicted by their Moiré fringes, crystals of hexagonal ice grow epitaxially on top of these domains along their [002] direction. In contrast, Ni anodes under similar electrochemical treatment do not form crystalline domains of the oxyhydroxides and therefore do not yield ice-nucleating surfaces.

By combining experimental data with density functional theory-based ab initio molecular dynamics modeling, this work provides evidence that nonclassical electrostriction in isovalent Zr-doped ceria is due to the correlated anharmonic motion of dynamic elastic dipoles associated with multiple [ZrO₈]-local bonding units with a high Zr concentration (Zr_0.1Ce_0.9O₂). Introduction of 0.5 mol % trivalent or divalent codopants (Sc, Yb, La, or Ca) reduces the longitudinal electrostriction strain coefficient by more than a factor of 10, produces a 3-fold decrease in the relative dielectric permittivity, and increases the elastic modulus. Since these changes depend neither on the radius nor on the valency of the codopant, we conclude that the responsible species are charge-compensating oxygen vacancies (V_O). For trivalent dopants (Do_0.005Zr_0.1Ce_0.895O_1.9975), oxygen vacancies are present at a concentration ratio 1:40 with respect to Zr, giving, for random distribution, a characteristic interaction distance of ≤2.3 unit cells (1.2 nm). Oxygen vacancies participate in [ZrO₇-V_O] local bonding units, disrupting the correlated dynamic displacements of the connected [ZrO₈]-local bonding units. Such correlated motion of dynamic elastic dipoles may also explain the exponential increase in the longitudinal electrostriction strain coefficient with an increase in Zr concentration to

Compositionally complex oxides (CCOs) or high-entropy oxides (HEOs) are new multielement oxides with unexplored physical and functional properties. In this work, we report fluorite structure-derived compositionally complex zirconia with composition Zr_1-x(Gd_1/5Pr_1/5Nd_1/5Sm_1/5Y_1/5)_xO_2−δ (x = 0.1 and 0.2) synthesized in solid-state reaction route and sintered via hot pressing at 1350 °C. We explore the evolution of these oxides structural, microstructural, mechanical, electrical, and electromechanical properties regarding phase separation and sintering mechanisms. Highly dense ceramics are achieved by bimodal mass diffusion, composing nanometric tetragonal and micrometric cubic grains microstructure. The material exhibits an anomalously large electrostriction response exceeding the M₃₃ value of 10^-17 m²/V² at room temperature and viscoelastic properties of primary creep in nanoindentation measurement under fast loading. These findings are strikingly similar to those reported for doped ceria and bismuth oxide derivates, highlighting the presence of a large concentration of point defects linked to structural distortion and anelastic behavior, which are characteristics of nonclassical ionic electrostrictors.

The local environments of Sc and Y in predominantly ⟨002⟩ textured, Al_1-xDo_xN (Do = Sc, x = 0.25, 0.30 or Y, x = 0.25) sputtered thin films with wurtzite symmetry were investigated using X-ray absorption (XAS) and photoelectron (XPS) spectroscopies. We present evidence from the X-ray absorption fine structure (XAFS) spectra that, when x = 0.25, both Sc³⁺ and Y³⁺ ions are able to substitute for Al³⁺, thereby acquiring four tetrahedrally coordinated nitrogen ligands, i.e., coordination number (CN) of 4. On this basis, the crystal radius of the dopant species in the wurtzite lattice, not available heretofore, could be calculated. By modeling the scandium local environment, extended XAFS (EXAFS) analysis suggests that when x increases from 0.25 to 0.30, CN for a fraction of the Sc ions increases from 4 to 6, signaling octahedral coordination. This change occurs at a dopant concentration significantly lower than the reported maximum concentration of Sc (42 mol % Sc) in wurtzite (Al, Sc)N. XPS spectra provide support for our observation that the local environment of Sc in (Al, Sc)N may include more than one type of coordination.

Electrostrictors, materials developing mechanical strain proportional to the square of the applied electric field, present many advantages for mechanical actuation as they convert electrical energy into mechanical, but not vice versa. Both high relative permittivity and reliance on Pb as the key component in commercial electrostrictors pose serious practical and health problems. Here we describe a low relative permittivity (= 0.02%. Combining X-ray absorption spectroscopy, atomic-level modeling and electromechanical measurements, here we show that electrostriction in ZrxCe1-xO2 is enabled by elastic dipoles produced by anharmonic motion of the smaller isovalent dopant (Zr). Unlike the elastic dipoles in aliovalent doped ceria, which are present even in the absence of an applied elastic or electric field, the elastic dipoles in ZrxCe1-xO2 are formed only under applied anisotropic field. The local descriptors of electrostrictive strain, namely, the cation size mismatch and dynamic anharmonicity, are sufficiently versatile to guide future searches in other polycrystalline solids.

This work reports that the octahedral hydrated Al³⁺ and Mg²⁺ ions operate within electrolytic cells as kosmotropic (long-range order-making) \u201cice makers\u201d of supercooled water (SCW). 10^-5 M solutions of hydrated Al³⁺ and Mg²⁺ ions each trigger, near the cathode (−20 ± 5 V), electro-freezing of SCW at −4 °C. The hydrated Al³⁺ ions do so with 100% efficiency, whereas the Mg²⁺ ions induce icing with 40% efficiency. In contrast, hydrated Na⁺ ions, under the same experimental conditions, do not induce icing differently than pure water. As such, our study shows that the role played by Al³⁺ and Mg²⁺ ions in water electro-freezing is impacted by two synchronous effects: (1) a geometric effect due to the octahedral packing of the coordinated water molecules around the metallic ions, and (2) the degree of polarization which these two ions induce and thereby acidify the coordinated water molecules, which in turn imparts them with an ice-like structure. Long-duration molecular dynamics (MD) simulations of the Al³⁺ and Mg²⁺ indeed reveal the formation of \u201cice-like\u201d hexagons in the vicinity of these ions. Furthermore, the MD shows that these hexagons and the electric fields of the coordinate water molecules give rise to ultimate icing. As such, the MD simulations provide a rational explanation for the order-making properties of these ions during electro-freezing.

We have investigated the synthesis, preparation protocols and properties of La(OH)3 powder and pellets. Preparation of useful pellet samples of La(OH)3 from the synthesized powder required (i) elimination of the presence of carbonate oxides by powder calcination at 1173 K in flowing oxygen; followed by (ii) hydration of the remaining La2O3 in boiling, deionized water for 48 h. Room temperature compaction of these powders into solid pellet samples with 73% of theoretical density, suitable for electrical measurements, requires prolonged (72 h) dwell under 80 MPa uniaxial pressure, suggesting that cold sintering and formation of inter-grain bridges do take place. The electrical conductivity (σ) of the compacted sample is an increasing function of temperature from 363 K to 463 K: evidence is presented that σ derives primarily from proton transfer. The activation energy in this temperature range is Ea ≈ 0.60 eV, while at 363 K, σ = 3·10−11 S/cm. Although 3·10−11 S/cm is too low for applications in fuel cells it may be sufficient for electro-chemo-mechanical applications. The fact that the grain boundaries are apparently not blocking, makes it attractive to look for dopants that may potentially enhance the low temperature conductivity. La(OH)3 powders were prepared via the carbonate route.La(OH)3powders were compacted into pellets by uniaxial pressing for 72 h.La(OH)3 ceramics exhibit electrical conductivity 3·10−11 S/cm at 363 K.Grain boundaries in La(OH)3ceramics are not blocking.

Electrostriction is a property of dielectric materials whereby an applied electric field induces a mechanical deformation proportional to the square of that field. The magnitude of the effect is usually minuscule (

The term \u201celectro-chemo-mechanical (ECM) effect\u201d describes mechanical deformation driven by an electrochemical reaction. Recently, an all-solid-state ECM device operating at room temperature was demonstrated. The device comprised a 20 mol% Gd-doped ceria (20GDC) self-supported electrolyte membrane placed between two mixed ionic/electronic conducting (MIEC) working bodies (WBs) constructed with TiO_x/20GDC nanocomposites. Actuation derived from volume change occurring upon oxidation/reduction of the WB. This raised the question of whether or not metal oxides other than TiO_x could be valuable components in MIEC nanocomposites functioning as WBs in ECM actuation. Here we examine the microstructure, crystal phase, oxidation state, chemical composition and ECM functionality of V-, Nb-, Mo-, Cu- and Ag-oxide/20GDC composite WBs prepared by co-sputtering. Of these, only the V-based composite was shown to be suitable for ECM actuation. According to X-ray absorption spectroscopy, the composition of the nanocomposite corresponds to VO_x/20GDC. Electrical characterization suggests that the formation of several coexisting VO_x nano-oxide phases is responsible for the longer response times as compared to TiO_x/20GDC WBs. ECM actuation demonstrated in the V-based system does indicate that composite WB based ECM is not unique to Ti and that this type of actuation constitutes a significant contribution to development of microelectromechanical systems.

Ceria (CeO₂) and its solid solutions with Gd₂O₃ are technologically important and environmentally friendly materials with numerous interesting properties and important applications. Nevertheless, the magnetic properties of ceria are even today not fully understood, and magnetoelastic coupling in pure or doped ceria remains essentially unexplored. This has been so, in part, due to the difficulty of measuring very small magnetostrictive strains in weakly paramagnetic materials. During the last decade, however, technical advances have enabled sensitive and accurate measurements of sample deformation in high magnetic fields. Here, forced magnetostriction (MS) in Gd₂O₃-CeO₂ solid solution ceramics (Ce_1−xGd_xO_2−x/2, 0 ≤ x ≤ 1) at room temperature is characterized. In a pulsed magnetic field μ₀H ≤ 60 Tesla, longitudinal MS strain is observed to depend on the square of the field amplitude and to increase linearly with Gd³⁺ concentration but is not sensitive to the lattice symmetry of the ceramics. The theory attributes the origin of the observed strain to the single-ion MS response of Gd³⁺ to the crystal field via mixing of ground and excited electronic states and covalent hybridization with oxygen ligands. Contributions of charge-compensating oxygen vacancies and/or Van Vleck paramagnetism to the observed magnetoelastic coupling are determined to be negligible.

Point defects such as oxygen vacancies and protonic interstitials are not only essential for ionic conductivity in oxides since they also affect the mechanical and electromechanical properties. These properties of nominally dry and hydrated proton-conducting BaZr0.85M0.15O2.925+δH2δ (M = Al, Ga, Sc, In, Y, Eu) ceramics are investigated. Doping decreases Young's modulus with increasing ionic radii difference between the dopant and the host. Nominally dry samples show consistently higher Young's moduli than hydrated samples. All samples exhibit large non-classical electrostriction, with a negative electrostriction coefficient M33

In functional materials, the local environment around active species that may contain just a few nearest-neighboring atomic shells often changes in response to external conditions. Strong disorder in the local environment poses a challenge to commonly used extended X-ray absorption fine structure (EXAFS) analysis. Furthermore, the dilute concentrations of absorbing atoms, small sample size and the constraints of the experimental setup often limit the utility of EXAFS for structural analysis. X-ray absorption near-edge structure (XANES) has been established as a good alternative method to provide local electronic and geometric information of materials. The pre-edge region in the XANES spectra of metal compounds is a useful but relatively under-utilized resource of information of the chemical composition and structural disorder in nano-materials. This study explores two examples of materials in which the transition metal environment is either relatively symmetric or strongly asymmetric. In the former case, EXAFS results agree with those obtained from the pre-edge XANES analysis, whereas in the latter case they are in a seeming contradiction. The two observations are reconciled by revisiting the limitations of EXAFS in the case of a strong, asymmetric bond length disorder, expected for mixed-valence oxides, and emphasize the utility of the pre-edge XANES analysis for detecting local heterogeneities in structural and compositional motifs.

We describe a laboratory-scale process for recycling rare earth metals from end-of-life rare-earth/iron/boron alloy permanent magnets using a 2-h chlorine gas treatment at 673 K. This treatment does not require any special preparation of the magnets; they can be used without demagnetization, crushing or milling. Following treatment at 673 K, a clinker powder consisting of rare earth metal chlorides with minimal amounts of other metals is obtained, while hematite and iron oxychloride sublimate. Following literature sources, we suggest that the rare earth metal chlorides in the clinker may be readily reduced to metal, either by electrolysis in relatively low temperature eutectic melts or by metallothermic reduction in mixtures with alkali or alkaline earth metals.

Minority hole diffusion length and lifetime were measured in independent experiments by electron beam-induced current and time-resolved cathodoluminescence in Si-doped β-Ga2O3 Schottky rectifiers irradiated with 18 MeV alpha particles and 10 MeV protons. Both diffusion length and lifetime exhibited a decrease with increasing temperature. The non-equilibrium minority hole mobility was calculated from the independently measured diffusion length and lifetime, indicating that the so-called hole self-trapping is most likely irrelevant in the 77-295 K temperature range.

Surface pyroelectricity and piezoelectricity induced by water incorporation during growth in α-glycine were investigated. Using the periodic temperature change technique, we have determined the thickness (~280 µm) of the near surface layer (NSL) and its pyroelectric coefficient (160 pC/(K × cm²) at 23^◦C) independently. The thickness of NSL remains nearly constant till 60^◦C and the pyroelectric effect vanishes abruptly by 70^◦C. The piezoelectric effect, 0.1 pm/V at 23^◦C measured with an interferometer, followed the same temperature dependence as the pyroelectric effect. Abrupt disappearance of both effects at 70^◦C is irreversible and suggests that water incorporation to α-glycine forms a well defined near surface phase, which is different form α-glycine because it is polar but it too close to α-glycine to be distinguished by X-ray diffraction (XRD). The secondary pyroelectric effect was found to be

Electrofreezing experiments of super-cooled water (SCW) with different ions, performed directly on the charged hemihedral faces of pyroelectric LiTaO(3)and AgI crystals, in the presence and in the absence of pyroelectric charge are reported. It is demonstrated that bicarbonate (HCO3-) ions elevate the icing temperature near the positively charged faces. In contrast, the hydronium (H3O+) slightly reduces the icing temperature. Molecular dynamics simulations suggest that the hydrated trigonal planar HCO(3)(-)ions self-assemble with water molecules near the surface of the AgI crystal as clusters of slightly different configuration from those of the ice-like hexagons. These clusters, however, have a tendency to serve as embryonic nuclei for ice crystallization. Consequently, we predicted and experimentally confirmed that the trigonal planar ions of NO(3)(-)and guanidinium (Gdm(+)), at appropriate concentrations, elevate the icing temperature near the positive and negative charged surfaces, respectively. On the other hand, the Cl(-)and SO(4)(2-)ions of different configurations reduce the icing temperature.

The impact of electron injection on minority carrier (hole) diffusion length and lifetime at variable temperatures was studied using electron beam-induced current, continuous, and time-resolved cathodoluminescence techniques. The hole diffusion length increased from 306nm to 347nm with an electron injection charge density up to 117.5nC/mu m(3), corresponding to the lifetime changing from 77ps to 101ps. Elongation of the diffusion length was attributed to the increase in the non-equilibrium carrier lifetime, which was determined using ultrafast time-resolved cathodoluminescence and related to non-equilibrium carrier trapping on gallium vacancy levels in the GaN forbidden gap.

We studied the stability of the mechanical properties and the fatigue endurance of Gd-doped ceria (CGO), which is a promising electromechanically active material for microelectromechanical systems (MEMS). Specifically, the fracture strength and long-term operation of plate-type circular (2 mm diameter) thermal actuators made of ≈1.15 μm thick Ce
_0.95Gd
_0.05O
_1.975 (CGO5) were investigated. Excitation voltage of 10 V at the frequency range between 1 and 2.1 MHz induces Joule heating effect that can generate an in-plane strain of ≈0.1 %. The operation temperature ranged from 25 °C to 80 °C and the temperature shift, caused by the AC heating, was about 80 K at 10 V. Critical fracture was found to occur at out-of-plane displacements between ∼35 and ∼42 μm, which corresponds to the average bending stress of ∼44 MPa at the center of the plate. During long-term operation, the actuators exhibit gradual decrease in the response, probably due to contact degradation. However, structural damage or mechanical fatigue was not found even after 10
⁷ cycles at a stress level of ∼30 % of the critical fracture strength.

Ceria and its solid solutions play a vital role in several industrial processes and devices. These include solar energy-to-fuel conversion, solid oxide fuel and electrolyzer cells, memristors, chemical looping combustion, automotive 3-way catalysts, catalytic surface coatings, supercapacitors and recently, electrostrictive devices. An attractive feature of ceria is the possibility of tuning defect-chemistry to increase the effectiveness of the materials in application areas. Years of study have revealed many features of the long-range, macroscopic characteristics of ceria and its derivatives. In this review we focus on an area of ceria defect chemistry which has received comparatively little attention - defect-induced local distortions and short-range associates. These features are non-periodic in nature and hence not readily detected by conventional X-ray powder diffraction. We compile the relevant literature data obtained by thermodynamic analysis, Raman spectroscopy, and X-ray absorption fine structure (XAFS) spectroscopy. Each of these techniques provides insight into material behavior without reliance on long-range periodic symmetry. From thermodynamic analyses, association of defects is inferred. From XAFS, an element-specific probe, local structure around selected atomic species is obtained, whereas from Raman spectroscopy, local symmetry breaking and vibrational changes in bonding patterns is detected. We note that, for undoped ceria and its solid solutions, the relationship between short range order and cation-oxygen-vacancy coordination remains a subject of active debate. Beyond collating the sometimes contradictory data in the literature, we strengthen this review by reporting new spectroscopy results and analysis. We contribute to this debate by introducing additional data and analysis, with the expectation that increasing our fundamental understanding of this relationship will lead to an ability to predict and tailor the defect-chemistry of ceria-based materials for practical applications.

The purpose of this study is to experimentally determine the effect of electron injection on the minority carrier lifetime in Gallium Nitride. Earlier studies of electron injection in GaN have provided an indirect proof of lifetime enhancement through the increase of minority carrier diffusion length and the decrease in the cathodoluminescence intensity. These changes in the minority transport properties, caused by electron injection, are brought forth through defect and trap levels in the bandgap. Furthermore, a thorough discussion of the electron injection model and role of these trap levels is presented.

Symmetry-imposed restrictions on the number of available pyroelectric and piezoelectric materials remain a major limitation as 22 out of 32 crystallographic material classes exhibit neither pyroelectricity nor piezoelectricity. Yet, by breaking the lattice symmetry it is possible to circumvent this limitation. Here, using a unique technique for measuring transient currents upon rapid heating, direct experimental evidence is provided that despite the fact that bulk SrTiO3 is not pyroelectric, the (100) surface of TiO2-terminated SrTiO3 is intrinsically pyroelectric at room temperature. The pyroelectric layer is found to be ≈1 nm thick and, surprisingly, its polarization is comparable with that of strongly polar materials such as BaTiO3. The pyroelectric effect can be tuned ON/OFF by the formation or removal of a nanometric SiO2 layer. Using density functional theory, the pyroelectricity is found to be a result of polar surface relaxation, which can be suppressed by varying the lattice symmetry breaking using a SiO2 capping layer. The observation of pyroelectricity emerging at the SrTiO3 surface also implies that it is intrinsically piezoelectric. These findings may pave the way for observing and tailoring piezo- and pyroelectricity in any material through appropriate breaking of symmetry at surfaces and artificial nanostructures such as heterointerfaces and superlattices.

CeO
₂ has a narrow, empty band of Ce 4f states that lies between an O 2p-based valence band and a Ce 5d-based conduction band. The O 2p-Ce 4f optical band gap is positioned at ∼3.2 eV with an absorption band centered at ∼3.8 eV. We investigated the Raman scattering of bulk CeO
₂ in the excitation energy range of 1.96-3.81 eV. The resonant enhancement profile of the longitudinal optical (LO) phonon at ∼590 cm
^-1 closely follows that of the 2LO band and both profiles track the optical absorption of the O 2p-Ce 4f electronic transition. Multi-LO phonon bands were found to appear up to the sixth order, pointing to an electron-phonon Fröhlich interaction as the source of the resonant enhancement. The ∼600 cm
^-1 off-resonant D
₂ band (denoted as MO
₈-type complex in ceria doped with M aliovalent ions) is overshadowed under resonant conditions by the resonant LO phonon scattering. Hence, spectral analysis of defect bands under resonant conditions has to be distinct from that applied under off-resonant conditions and care must be taken when dealt with under a single framework. We investigated the resonant Raman spectra of Lu-, La-, Gd-, or Sm-doped ceria ceramic pellets as a function of increasing Do
³⁺ mol %, in the fluorite phase range (up to 20 mol %). For La and Lu, the general trend of the Do
³⁺ mol % frequency dependence for the D
₁ local mode is qualitatively similar to that of the F
_2g phonon and it follows the respective expansion (La) or contraction (Lu) in the lattice parameter. However, for Gd and Sm, the trend is opposite to the F
_2g mode. This trend may stem from local lattice contraction around point defects, which was suggested, based on local structure probes such as X-ray absorption spectroscopy and pair distribution function analysis of X-ray diffraction. Our analysis provides access to average as well as to local structures of ceria solid solutions, via resonant Raman spectroscopy.

Some oxygen defective metal oxides, such as cerium and bismuth oxides, have recently shown exceptional electrostrictive properties that are even superior to the best performing lead-based electrostrictors, e.g. lead-magnesium-niobates (PMN). Compared to piezoelectric ceramics, electromechanical mechanisms of such materials do not depend on crystalline symmetry but on the concentration of oxygen vacancy (V
_O
^⋅⋅) in the lattice. In this work, we investigate for the first time the role of oxygen defects configuration on the electro-chemo-mechanical properties. This is achieved by tuning the oxygen defects blocking barrier density in polycrystalline gadolinium doped ceria with known oxygen vacancy concentration, Ce
_0.9Gd
_0.1O
_2-δ, δ = 0.05. Nanometric starting powders of ca. ∼12 nm are sintered in different conditions, including field assisted spark plasma sintering (SPS), fast firing and conventional method at high temperatures. These approaches allow controlling grain size and Gd-dopant diffusion, i.e. via thermally driven solute drag mechanism. By correlating the electro-chemo-mechanical properties, we show that oxygen vacancy distribution in the materials plays a key role in ceria electrostriction, overcoming the expected contributions from grain size and dopant concentration.

Ceria doped with trivalent dopants exhibits nonclassical electrostriction, strong anelasticity, and room-temperature (RT) mechanical creep. These phenomena, unexpected for a ceramic material with a large Young's modulus, have been attributed to the generation of local strain in the vicinity of the host Ce cations due to symmetry breaking point defects, including oxygen vacancies. However, understanding why strain is generated at the host rather than at the dopant site, as well as predicting these effects as a function of dopant size and concentration, remains a challenge. We have used the, evolutionary-algorithm-based reverse Monte Carlo modeling to reconcile the experimental data of extended X-ray absorption fine structure and X-ray diffraction in a combined model structure. By extracting the details of the radial distribution function (RDF) around the host (Ce) and trivalent dopants (Sm or Y), we find that RDF of the first-nearest neighbor (1NN) of host and dopant cations as well as the second-nearest neighbor (2NN) of the dopant are each best modeled with two separate populations corresponding to short and long interatomic distances. This heterogeneity indicates that fluorite symmetry is not preserved locally, especially for the dopant first-and second-NN sites, appearing at surprisingly low doping fractions (5 mol % Sm and 10 mol % Y). Given that Ce rather than dopant sites act as the source of local strain for electrostriction and RT creep, we conclude that the environment around the dopant does not respond to electrical and mechanical excitations, likely because of its similarity to the double fluorite structure which has poor electrostrictive and anelastic properties. The trends we observe in the RDFs around the Ce sites as a function of dopant size and concentration suggest that the response of these sites can be controlled by the extent of doping: Increasing dopant size to increase strain magnitude at the 1NN shell of Ce and decreasing dopant fraction to decrease strain propagation to the 2NN shell of Ce should produce stronger electrostrictive response and RT creep.

A protocol for characterizing relaxation of anisotropic strain in thin films of 10 mol% Eu- or Sm-doped ceria is described. The method is based on comparison of Raman spectra and X-ray diffraction patterns from substrate-supported films, displaying in-plane compressive strain (initial state), with analogous data from 2 mm diameter self-supported films (i.e., membranes), prepared by partial substrate removal (final state). These membranes are found to be relaxed, i.e., approximately unstrained, but with increased unit cell volume. The effective (i.e., 2-state) Gruneisen parameter of the F-2g Raman active mode for these films is calculated to be 0.4 +/- 0.1, which is approximate to 30% of the literature value for the corresponding ceramics under isostatic pressure. On this basis, it is found that the observed red-shift of the F-2g mode frequency following isothermal strain relaxation of the doped ceria thin films cannot be determined solely by the increase in average unit cell volume. The study presented here may shed light on the suitability of Raman spectroscopy as a technique for characterizing strain in lanthanide-doped ceria thin films.

The electrical conductivity of Ce
_0.90Gd
_0.10O
_1.95 oxide ion conductor is studied, emphasizing distribution function of relaxation times (DFRT) analysis of impedance spectroscopy measurements. The corresponding powder has been prepared by co-precipitation method and sintered at 1300 °C. The formation of the fluorite phase is confirmed by X-ray diffraction. The temperature dependence of ionic conductivity has been studied at different bias voltages. The impedance spectra are analysed by impedance spectroscopy genetic programming (ISGP) that finds an analytic form of the DFRT. Interestingly, both the grain and grain boundary conductivities can be identified at room temperature by analysing the DFRTs. At higher temperatures and higher bias voltages, the grain boundary diffusion process of oxygen ions is identified. Both the grain and grain boundary activation energies are bias independent.

Ionic current in proton-conducting polycrystalline ceramics is often hampered a great deal by the grain boundaries, limiting their prospective applications as solid electrolytes for next-generation solid oxide fuel cells. To elucidate the conduction mechanism at the grain boundaries, we use a linear diffusion model and impedance spectroscopy to report complete current-voltage (I-V) characteristics of the grain boundaries in 0.5 mol % Sr-doped LaNbO4. We provide the first experimental evidence of complete annihilation of the space charge-induced proton depletion at the grain boundaries upon applying moderate bias voltages. We also show that it is possible to distinguish between the grain boundary resistance caused by the space charge and other sources by analyzing the I-V characteristics. The analysis is equally valid for other solid ionic conductors such that it can serve as an important tool to guide further optimization of the conductivity of polycrystalline solid electrolytes.

We report on a rapid sintering protocol, which optimizes the preparation of 0-29 mol% Gd-doped ceria ceramics with density ≥98% of the theoretical crystal lattice value. The starting material is a nanometer grain-sized powder prepared by carbonate co-precipitation and calcined with minimal agglomeration and loss of surface area. Slow (5°C/min) heating of the green-body from 500°C to the optimum temperature of rapid sintering ((Formula presented.), dwell time

Acceptor doped BaZrO
₃ is the prototype of proton conducting perovskites which are of strong interest as electrolytes for intermediate temperature fuel cells. Elastic properties of both dry and hydrated Y-doped BaZrO
₃ (1.517 mol% Y) were determined using ultrasound time of flight (TOF) measurements, and complemented by ab initio calculations which allow for an analysis of the different contributions. The experimental and theoretical findings are consistent and reveal a strong decrease of the Young's, shear and bulk moduli upon increasing dopant concentration. This decrease is attributed to a combined effect of (i) macroscopic lattice chemical expansion mainly caused by differing ionic radii, and (ii) presence of point defects such as acceptors Acc
_Zr
(with decreased cation charge), oxygen vacancies V
_O
, and protonic defects OH
_O
(hydroxide ions on oxide ion sites) that locally weaken the chemical bonds in the perovskite structure. The effect from modified lattice parameter is minor relative to the decrease in moduli caused by Acc
_Zr
, V
_O
, OH
_O
weakening the chemical bonds. The elastic moduli differ only slightly between the dehydrated and hydrated samples. The decrease in the elastic moduli with increasing acceptor and oxygen vacancy concentrations is much stronger in Y-doped BaZrO
₃ (−5.8% in Y:BaZrO
₃ per mol% of vacancies) compared to similar earlier investigations on Gd-doped CeO
₂ (−2% in Gd:CeO
₂). This result indicates a greater effect of oxygen vacancies on the elastic properties in ABO
₃ perovskites with the linear BOB bonds as compared to fluorites with strongly bent M-O-M bonds.

The dissolution enthalpy, ΔH
_DS, and the formation enthalpy, ΔH
_f,ox, of bulk lutetium-doped cerium oxide (LuDC) were studied at 701°C in molten sodium molybdate. For the composition range of Ce
_1−XLu
_XO
_2−X/2, studied 0 ≤ X ≤ 0.3, the ΔH
_DS decreases linearly and smoothly with lutetium content according to ΔH
_DS, kJ/mol = 73.5(1.0)−165.1(5.5)·x). The enthalpy of formation, ΔH
_f,ox, becomes more exothermic linearly with lutetium content. No anomaly in ΔH
_f,ox is observed at low Lu
₂O
₃ concentration as reported previously for several other rare-earth-doped ceria systems, suggesting possible differences in clustering and microstructure, which may also be related to difference in processing conditions.

The pyroelectricity of AgI crystals strongly affects the icing temperature of super-cooled water, as disentangled from that of epitaxy. This deduction was achieved by the design of polar crystalline ceramic pellets of AgI, with experimentally determined sense of polarity. These pellets are suitable for measuring both their pyroelectric properties as well as the icing temperature of super-cooled water, separately on each of the expressed Ag+ and I- hemihedral surfaces. The positive pyroelectric charge at the silver-enriched side elevates the icing temperature, whereas the negative charge at the iodide side decreases that temperature. Moreover, the effect of pyroelectric charge remains dominant despite the presence of contaminants on both the silver and the iodide-enriched surfaces. Consequently an electrochemical process for ice nucleation is suggested, which might be of relevance for understanding the role played by electric charges in heterogeneous icing processes in general.

The extent of the influence of space charge on the electric current through the grain boundary in solid electrolytes can be parameterized by the grain boundary potential, i.e. the height of the potential barrier formed at the grain boundary. Previously the value of this parameter has been estimated exclusively by the ratio of the grain boundary resistivity to the bulk counterpart over several decades. We recently demonstrated that it can be alternatively determined by analyzing the current-voltage characteristic of the grain boundary. Furthermore, we theoretically justified that the conventional method is in fact a subset of the new method, therefore, the latter is a more reliable and comprehensive approach to determine the grain boundary potential. Here, we present the experimental results that verify our theoretical justification. The values of the grain boundary potential determined for 1 mol% Sr-doped LaGaO3 (LSG1) employing both methods are in excellent agreement with one another. Such a consistency has not been reported for other solid electrolytes to date and we provide an explanation for it. Our data also indicate that for the case of LSG1, the Nernst-Einstein relation is preserved at the electric field exceeding 900 kV cm(-1).

Metastable polymorphs commonly emerge when the formation of the stable analogues is inhibited by using different solvents or auxiliaries. Herein, we report that when glycine is grown in aqueous solutions in the presence of low concentrations of different co-solvents, only alcohols and acetone, unlike water and acetic acid, are selectively incorporated in minute amounts within the bulk of the α-polymorph. These findings demonstrate that although water binds more strongly to the growing face of the crystal, alcohols and acetone are exclusively incorporated, and thus serve as efficient inhibitors of this polymorph, leading to the precipitation of the β-form. These solvents then create polar domains detectable by pyroelectric measurements and impedance spectroscopy. These results suggest that in the control of crystal polymorphism with co-solvents, one should consider also the different desolvation rates in addition to the energy of binding to the growing faces of the crystal.

We show that platinum (Pt) and palladium (Pd) can be efficiently removed from spent catalytic converters by means of a sintering process involving chloride salts. For Pt, mixing the crushed catalyst in an aqueous solution of chloride salts at catalyst/salt weight ratios ranging from 2.5 to 6.7, followed by drying, and 2-h sintering in the reactor furnace at 1100 degrees C, results in extraction of 80 +/- 4% of the metal. For Pd, the addition of fumed silica to the dry chlorination agents was necessary in order to optimize extraction using fractional factorial design of experiments (DOE). Maximum Pd extraction of 93 +/- 5% was achieved at 1100 degrees C with weight ratios of the catalyst material: CaCl2.2H(2)O:SiO2 = 1:0.6:1.2. Application of a similar protocol to Pt-containing catalytic converters would be expected to result in a similar high level of extraction efficiency. The primary advantage of the proposed extraction process is that it does not involve hazardous chemicals, strong bases/acids, or corrosive gases, and produces, as a byproduct, only small quantities of nontoxic silicate waste.

In this study, we explored the feasibility of employing Gd-doped ceria (GDC) thin films (12 μm) as functional, mechanically reliable material for microelectromechanical systems (MEMS). Self-supported structures, based on microscopic-scale GDC membranes, bridges, and cantilevers, were fabricated using Si-compatible processes and materials. With voltages of different amplitudes and frequencies and a variety of metal electrodes, we monitored structural stability and device response. The membrane-based structures displayed much higher stability under voltage and better mechanical robustness than those based on bridges or cantilevers. At low frequencies (a few Hz), the use of Ti contacts resulted in observable displacement of the membranes in the presence of moderately low voltage (≤10 V/1.6 μm), while Al, Cr, and Ni contacts did not provide such functionality. Although for all contact metals tested, formation of a blocking layer at room temperature is evident, for the case of Ti, the barrier height is much lower. In view of the fact that the crystallographic space group of weakly doped GDC is Fm-3 m, the electromechanical response of the microfabricated GDC membranes is most likely electrostrictive, but a strict proof is not yet available. At high frequencies (>100 kHz), the membranes produce lateral displacement as large as several microns due to Joule heating, i.e., a thermo-electromechanical response.

Halide perovskite (HaP) semiconductors are revolutionizing photovoltaic (PV) solar energy conversion by showing remarkable performance of solar cells made with HaPs, especially tetragonal methylammonium lead triiodide (MAPbI₃). In particular, the low voltage loss of these cells implies a remarkably low recombination rate of photogenerated carriers. It was suggested that low recombination can be due to the spatial separation of electrons and holes, a possibility if MAPbI₃ is a semiconducting ferroelectric, which, however, requires clear experimental evidence. As a first step, we show that, in operando, MAPbI₃ (unlike MAPbBr₃) is pyroelectric, which implies it can be ferroelectric. The next step, proving it is (not) ferroelectric, is challenging, because of the material's relatively high electrical conductance (a consequence of an optical band gap suitable for PV conversion) and low stability under high applied bias voltage. This excludes normal measurements of a ferroelectric hysteresis loop, to prove ferroelectricity's hallmark switchable polarization. By adopting an approach suitable for electrically leaky materials as MAPbI₃, we show here ferroelectric hysteresis from well-characterized single crystals at low temperature (still within the tetragonal phase, which is stable at room temperature). By chemical etching, we also can image the structural fingerprint for ferroelectricity, polar domains, periodically stacked along the polar axis of the crystal, which, as predicted by theory, scale with the overall crystal size. We also succeeded in detecting clear second harmonic generation, direct evidence for the material's noncentrosymmetry. We note that thematerial's ferroelectric nature, can, but need not be important in a PV cell at room temperature.

Sulfur emission in the form of SO₂ in flue gases is the one of the most serious atmospheric pollutants associated with coal combustion and non-ferrous metal production. The carbonate eutectic method for removing SO₂ from flue gases at 723-923 K was initially proposed in the 1970's but despite its great efficiency (SO₂ concentration in the flue gas after purification reached 0.003 vol%) it could not be implemented by industry due to the complexity of the carbonate melt regeneration stage. Earlier we proposed a method suited to coal-firing power stations where the melt was regenerated using CO as a reducing agent. However, most metallurgical plants do not use coal and therefore lack a large source of CO. Here we propose a method for removing sulfur from the carbonate eutectic melt by purging it with natural gas or a natural gas/air mixture, which are available in the vast majority of metallurgical plants. This reaction leads to the reduction of sulfate to H₂S gas that leaves the melt. The experiments we conducted show that nearly complete sulfur removal from the melt is possible at 823 K and that the reaction rate is sufficiently high for a large scale process. The proposed modifications provide solutions to two major problems previously encountered: (i) high temperature corrosion of the reaction cell can be avoided, since a stainless steel cell with high chromium content is stable with respect to the carbonate eutectic melt at 823 K, and (ii) removal of sulfur in the form of H₂S provides considerable freedom in choosing the final industrially useful product: either sulfuric acid, using H₂S dry combustion, or elemental sulfur via the Claus process. One can foresee that this carbonate melt-based SO₂ removal technique may become a practical and economically attractive method for limiting sulfur emission to the atmosphere from non-ferrous metallurgical processing plants.

Here we present the results of the study of electromechanical performance of the Ce0.8Gd0.2O1.95 (CGO) self-supported thin circular membranes with aluminum and titanium as contact electrode materials. The electromechanical performance of both membranes was investigated using highly sensitive interferometric technique and showed two principal excitations mechanisms: common electrostriction and thermal contribution due to the Joule heating. Operating the membranes at frequencies about MHz results in significant contribution of the thermal excitation due to a large power dissipation for every electrode. The excitation of the membrane with aluminum electrodes at the frequencies about 1 Hz leads to the formation of the Schottky barrier at the interface with CGO. That is why the electromechanical response was almost independent on frequency and electric field. Membrane with titanium electrodes showed a prevalence of electrostriction effect with weak frequency dispersion and significant enhancement of the response with temperature.

The riddle of anomalous polar behavior of the centrosymmetric crystal of α-glycine is resolved by the discovery of a polar, several hundred nanometer thick hydrated layer, created at the {010} faces during crystal growth. This layer was detected by two independent pyroelectric analytical methods: (i) periodic temperature change technique (Chynoweth) at ambient conditions and (ii) contactless X-ray photoelectron spectroscopy under ultrahigh vacuum. The total polarization of the surface layer is extremely large, yielding ≈1 μC·cm^-2, and is preserved in ultrahigh vacuum, but disappears upon heating to 100 °C. Molecular dynamics simulations corroborate the formation of polar hydrated layers at the sub-microsecond time scale, however with a thickness of only several nanometers, not several hundred. This inconsistency might be reconciled by invoking a three-step nonclassical crystal growth mechanism comprising (i) docking of clusters from the supersaturated solution onto the evolving crystal, (ii) surface recognition and polar induction, and (iii) annealing and dehydration, followed by site-selective recrystallization.

Quasi-amorphous films are the only known inorganic, non-crystalline, polar materials. The conditions under which they are formed and the origin of their polarity set these materials apart from other classes of inorganic materials. The unique feature of the quasi-amorphous phase is that its polarity is the result of flexoelectric-induced orientational ordering of local bonding units without any detectable spatial periodicity. However, unlike classical flexoelectricity - the reversible coupling of polarity and strain gradients - the strain gradient imposed on quasiamorphous films leads to permanent polarization, i.e. the polarization is retained even after the strain gradient has been eliminated. This mechanism permits compounds that do not have polar crystalline polymorphs, such as SrTiO₃ and BaZrO₃, to form polar, non-crystalline solids. In this chapter, we describe the essential features of quasiamorphous materials including preparation, structure, and chemical composition.

Local distortions from average structure are important in many functional materials, such as electrostrictors or piezoelectrics, and contain clues about their mechanism of work. However, the geometric attributes of these distortions are exceedingly difficult to measure, leading to a gap in knowledge regarding their roles in electromechanical response. This task is particularly challenging in the case of recently reported non-classical electrostriction in Cerium-Gadolinium oxides (CGO), where only a small population of Ce-O bonds that are located near oxygen ion vacancies responds to external electric field. We used high-energy resolution fluorescence detection (HERFD) technique to collect X-ray absorption spectra in CGO in situ, with and without an external electric field, coupled with theoretical modeling to characterize three-dimensional geometry of electromechanically active units.

Classical electrostriction, describing a second-order electromechanical response of insulating solids, scales with elastic compliance, S, and inversely with dielectric susceptibility, ε. This behavior, first noted 20 years ago by Robert Newnham, is shown to apply to a wide range of electrostrictors including polymers, glasses, crystalline linear dielectrics, and relaxor ferroelectrics. Electrostriction in fluorite ceramics of (Y, Nb)-stabilized δ-Bi₂O₃ is examined with 16%-23% vacant oxygen sites. Given the values of compliance and dielectric susceptibility, the electrostriction coefficients are orders of magnitude larger than those expected from Newnham's scaling law. In ambient temperature nanoindentation measurements, (Y, Nb)-stabilized δ-Bi₂O₃ displays primary creep. These findings, which are strikingly similar to those reported for Gd-doped ceria, support the suggestion that ion conducting ceramics with the fluorite structure, a large concentration of anion vacancies and anelastic behavior, may constitute a previously unknown class of electrostrictors.

Highly sensitive laser interferometer was built to measure electromechanical coupling in Gd-doped ceria Ce0.9Gd0.1O2-x thin films in the frequency range up to 20 kHz. Spurious resonances due to substrate bending were avoided by the special mounting of the film in the center of substrate. Compact design allowed to reach high vertical resolution of about 0.2 pm. Electrostriction coefficient measured in 1 mu m thick Ce0.9Gd0.1O2-x film was 4.3x10(-21)m(2)/V-2 and slightly decreased with frequency till the extensional resonance of the substrate at about 20 kHz occurred. As expected, the displacement varied as a square of applied voltage without any sign of saturation. A comparison with ceramics showed much higher electrostriction coefficient in the latter in the same frequency range.

An electrochemical cell containing molten Li₂CO₃-Li₂O has been proposed for the conversion of the greenhouse gas CO₂ to CO, which can then either be used to power gas turbines or converted to methanol. Since efficient electrolysis takes place at 900°C, the materials which can be used in such a cell must satisfy stringent requirements. In the current work, we have examined the static corrosion resistance of zirconia, beryllia and magnesia ceramics at 900 °C in the Li₂CO₃-Li₂O mixture and in a Li-Na-K carbonate eutectic mixture with the ultimate objective of identifying suitable electrically insulating materials. Conclusions regarding material stability were based on elemental analysis of the melt, primarily via X-ray photoelectron spectroscopy, a particularly sensitive technique. It was found that magnesia is completely stable for at least 33 hrs in a Li₂CO₃-Li₂O melt, while a combined lithium titanate/lithium zirconate layer forms on the zirconia ceramic as detected by XRD. Under the same melt conditions, beryllia shows considerable leaching into solution. In a Li-Na-K carbonate eutectic mixture containing 10.2 mol% oxide at 900°C under standard atmospheric conditions, magnesia showed no signs of degradation. Stabilization of the zirconia content of the eutectic mixture at 0.01-0.02 at% after 2 hrs is again explained by the formation of a lithium titanate/ lithium zirconate coating. On the basis of these results, we conclude that only magnesia can be satisfactorily used as an insulating material in electrolysis cells containing Li₂CO₃-Li₂O melts.

The effects of ⁶⁰Co gamma-irradiation on AlGaN/GaN High Electron Mobility Transistors (HEMTs) were studied by means of temperature dependent Cathodoluminescence (CL). The CL spectra were examined for several devices with radiation exposures of gamma-ray doses up to 1000 Gy, and for temperature ranging from 25°C to 125°C. Gamma-irradiation causes the CL intensity of HEMTs to decrease by creating defects that act as non-radiative recombination centers. The activation energy was observed to decrease as dosage was incremented to 200 Gy. The decrease in activation energy is related to Compton electron induced increase in carrier lifetime. However for doses above 200 Gy, the activation energy increases as the dose increases. This behavior could be explained by the formation of large electrically active defect complexes through the addition of new radiation defects to the defects formed at low doses.

Abstract We describe the use of null-ellipsometry with lock-in detection to monitor grain core oxygen diffusion in thin films of the solid-state ionic conductor Ce_0.8Gd_0.2O_1.9. Application of an electric field perpendicular to the film surface - probe alternating voltage (U_A) in addition to perturbation bias voltage (U_B) - produces ellipsometer optical response at the probe frequency. The signal amplitude and time dependence can be interpreted in terms of changes in the local material polarizability. Since the ionic contribution to the material polarizability is much larger than that of electrons or protons, the diffusion of ions can be distinguished. Because grain cores occupy the majority of the film volume, ion diffusion in the grain cores dominates the optical response. This effect was studied as a function of temperature (75-160°C), amplitude and frequency of the electric field. The activation energy for oxygen diffusion in the grain cores was found to be 1.1 ± 0.1 eV and 1.5 ± 0.1 eV for films with in-plane compressive strain of 0.34 ± 0.06% and in-plane tensile strain 0.16 ± 0.03%, respectively.

We describe a technique for measuring the activation energy of ion diffusion in ionic and mixed ionic/electronic conductors. The technique is based on monitoring small changes in refractive index near the interface of a semitransparent gold electrode with the sample surface. Constant bias voltage is applied to the sample to weakly perturb the distribution of charge carriers near this front electrode. The relaxation process induced by bias removal is probed by applying alternating voltage and monitoring by ellipsometry with lock-in detection the changes in the refractive index dominated by changes in material polarizability. Since the ionic contribution to the total material polarizability is much larger than that of electrons or protons, the diffusion of ions can be distinguished. Measurements were made as a function of temperature on single crystals of 8 mol% Y-stabilized zirconia (YSZ8), on ceramic pellets of 20 mol% Gd doped CeO₂ (GDC20) and on single crystals of 0.03 mol% Fe-doped SrTiO₃ (Fe-STO). In YSZ8, a single moving species (oxygen vacancies) with activation energy of 0.8 eV was detected. The "wet" and "dry" states of GDC20 can be clearly distinguished: in the "wet" state there are mobile species other than oxygen vacancies, most likely protons. In Fe-doped SrTiO₃, the proposed technique can reliably measure the activation energy of oxygen ion diffusion on a background of the much larger electronic conductivity.

We demonstrate the applicability of the linear diffusion model recently proposed for the current-voltage, I_gb-U_gb, characteristics of blocking grain boundaries in solid electrolytes to various oxygen-ion and proton conductors: the model precisely reproduces the I_gb-U_gb characteristics of La-, Sm-, Gd-, and Y-doped ceria as well as Y-doped barium zirconate to provide accurate explanations to the \u201cpower law\u201d behavior of the I_gb-U_gb relationship, i.e. I_gb∝U_gbⁿ, experimentally observed. The model also predicts that the grain-boundary potential, Ψ_gb, in doped ceria weakly depends on temperature, if the trapped charge remains constant, and that the value of Ψ_gb can be determined from the value of the power n. Furthermore, the model provides a plausible explanation for the increase in the Ψ_gb with temperature observed for the proton conductor in which the concentration of the charge carrier decreases with temperature. Hence, it is evident that the linear diffusion model is robust and applicable to grain boundaries in a large variety of practically important solid electrolytes.

AlGaN/GaN High Electron Mobility Transistors were irradiated with Co-60 gamma-ray doses from 100 Gy up to a maximum dose of 1000 Gy. After irradiation, the devices were annealed at 200 degrees C for 25 minutes. Annealing of the gamma irradiated transistors show that partial recovery of device performance is possible at this temperature. The impact of irradiation and annealing on minority carrier diffusion length and activation energy were monitored through the use of the Electron Beam Induced Current method. Impact on transfer, gate, and drain characteristics were analyzed through current-voltage measurements.

Sulfur emission in the form of SO₂ in flue gas is the most serious pollutant associated with coal combustion. Calcium carbonate sulfur scrubbing, the process most commonly in use today, is costly, produces a large amount of waste and leaves a considerable amount of SO₂ in the gas. The carbonate eutectic method for removing SO₂ from flue gas at 450-650 °C was initially proposed in the 1970's but despite its great efficiency could not be used due to the complexity of the carbonate melt regeneration stage. We propose a simple way to remove sulfur from the carbonate eutectic melt by purging it with CO. In contrast to expectation, this reaction leads to the reduction of sulfate to carbonyl sulfide gas that leaves the melt, rather than to sulfide ions that remain in the melt. The experiments conducted show that nearly complete sulfur removal from the melt is possible at 550 °C and that the reaction rate is sufficiently high for a large scale process. The proposed modifications provide solutions to two critical issues: (i) at 550 °C there is no problem of corrosion because a reaction cell of stainless steel with high chromium content is stable with respect to the carbonate eutectic melt at that temperature and (ii) removal of sulfur in the form of COS, rather than H₂S, provides considerable freedom in choosing the final product: either sulfuric acid or elemental sulfur. In addition, we verified that fly ash does not dissolve in the carbonate eutectic melt and therefore will not interfere with SO₂ removal. One can foresee that the carbonate melt-based SO₂ removal technique may become a practical and viable method for limiting sulfur emission to the atmosphere.

Surface pyroelectricity: Centrosymmetric crystals of α-glycine display an anomalous quadrupole-like pyroelectric current. This observation implies the formation of water-glycine hybrid polar layers at the (010) faces of the α-glycine crystals (see picture).

Dr Williams (AIP Adv., 2012, 2, 010701) suggested that cleaning Teflon by high pressure oxygen plasma may have affected our result that Cu ²⁺ and Pd ²⁺ ions can be absorbed but not chemically reduced by a Teflon surface rubbed by PMMA (Phys. Chem. Chem. Phys., 2012, 14, 5551). In response, we show that this treatment does not affect the adsorption of Cu ²⁺ and Pd ²⁺. We reaffirm our statement that Cu ²⁺ and Pd ²⁺ ions can be adsorbed by a Teflon surface only after rubbing with the organic polymers, not before rubbing.

The characterization of pyroelectric materials is a necessary stage in the design of a large variety of pyroelectric-based devices ranging from intrusion alarms to IR cameras. The sample configurations and measurement techniques currently in use vary widely and require careful attention in order to avoid artifacts. In this review, we provide a practical guide to the measurement of the pyroelectric coefficient, paying particular attention to the new instrumental possibilities (fast sinusoidally modulated light sources, low impedance broad band current meters, and fast averaging oscilloscopes) that have become available during the last decade. Techniques applicable to bulk specimens, substrate-supported films, and self-supported films are described in detail. The most commonly used procedures are classified according to the type of thermal excitation: continuous ramping, heat pulse, and continuous oscillation. In the appendices, we describe the practical realization of these measurement schemes and provide mathematical descriptions for the extraction of the pyroelectric coefficient from the measured data.

It has recently been reported that Teflon and polyethylene (PE) if rubbed by polymethylmethacrylate (PMMA) or Nylon as well as non-rubbed PMMA and Nylon induce "redox" reactions, including those of the reduction of Pd ⁺² and Cu ⁺² ions. On this basis, it was deduced that these dielectric materials may hold ≅10 ¹³-10 ¹⁴ of "hidden" electrons cm ^-2, a value at least three orders of magnitude higher than the charge that a dielectric surface can accumulate without being discharged in air. The "hidden" electrons were termed "cryptoelectrons". In variance to these reports, we offer here an alternative interpretation. Our model is supported by X-ray photoelectron spectroscopy, contact angle and vibrating electrode (modified Kelvin probe) measurements performed on representative examples. Rubbing of the polymers was found to transfer polymer fragments between the rubbed surfaces altering their physical properties. The transferred polymer fragments promote adsorption of Cu ²⁺ and Pd ²⁺ ions. It was found that Teflon and PE rubbed with PMMA and Nylon, and non-rubbed PMMA and non-rubbed Nylon do not induce "redox" reactions of Cu ²⁺ and Pd ²⁺ ions but adsorb these ions on their surfaces. Furthermore, the earlier reported reduction of Pd ²⁺ to Pd ⁰ by electrons, as detected by catalytic activity of Pd ⁰ in a Cu-plating bath, can be alternatively explained by reduction of adsorbed Pd ²⁺ by the reducing agents of the bath itself. Based on these findings, we support the hypothesis that charging of dielectric polymers is due to ions or free radicals rather than electrons and there is no evidence to invoke a hypothesis of "cryptoelectrons".

High-density ceramics of ceria doped with 0, 3, 5, 10, 15 and 20 mol.% Gd and with grain sizes exceeding 1.5 μm were investigated by nanoindentation. The deduced elastic moduli are independent of Gd content and remain close to the value reported for bulk ceramics (210 ± 5% GPa). All ceramics exhibit transient creep with displacement proportional to the 1/3 power of the time. For 0.05

The presence of water at the surface of sputtered thin films of Ce _0.8Gd_0.2O_1.9, which display elastic anomalies as a function of thermal treatment, and of stoichiometric CeO₂ films, which do not, was monitored using X-ray photoelectron spectroscopy. We find that considerably more water is strongly bound at the surface of the Ce _0.8Gd_0.2O_1.9 films than of the CeO₂ films. This supports the theoretical prediction that water binds preferentially at the oxygen vacancy sites. In addition, all films were treated according to the protocol which has been shown to produce inelastic behavior in the doped films: annealed at 500 °C, exposed to ambient atmosphere for one month and then heated to 250 °C in ultra-high vacuum. Neither the Ce _0.8Gd_0.2O_1.9 nor the CeO₂ films show any change in the amount of adsorbed water. We therefore conclude that changes in the amount of surface adsorbed water do not play a role in the elastic anomalies observed as a function of thermal treatment of Ce_0.8Gd _0.2O_1.9 films.

Rub-a-dub-dub: The hypothesis of contact electrification through the transfer of cryptoelectrons was tested by scrutinizing the evidence for the reduction of Pd²⁺ and Cu²⁺ by static charges on rubbed Teflon. X-ray photoelectron spectroscopy studies indicated that neither of these ions is reduced (see picture; black: Pd²⁺ adsorbed, red: Pd ⁰ adsorbed and then reduced by formadehyde, green: mixture of Pd ²⁺ and Pd⁰ arising from partial reduction after 2 h under the XPS probe) by the static charge. The presented alternative interpretation challenges the role of cryptoelectrons.

Quasi-amorphous thin films of BaTiO₃, SrTiO₃, and BaZrO₃ are the only known examples of inorganic, non-crystalline, polar materials. The conditions under which they are formed and the origin of their polarity set these materials apart from other classes of inorganic materials. The most important feature of the quasi-amorphous phase is that the polarity is the result of the orientational ordering of local bonding units but without any detectable spatial periodicity. This mechanism is reminiscent ofthat observed in ferroelectric polymers and permits compounds that do not have polar crystalline polymorphs, such as SrTiO₃ and BaZrO₃, to form polar noncrystalline solids. In the present report, we provide an overview of the essential features of these materials including preparation, structure, and chemical composition. The report also reviews our current level of understanding and offers some guidelines for further development and application of non-crystalline inorganic polar materials.

Although ice melts and water freezes under equilibrium conditions at 0°C, water can be supercooled under homogeneous conditions in a clean environment down to -40°C without freezing. The influence of the electric field on the freezing temperature of supercooled water (electrofreezing) is of topical importance in the living and inanimate worlds. We report that positively charged surfaces of pyroelectric LiTaO₃ crystals and SrTiO ₃ thin films promote ice nucleation, whereas the same surfaces when negatively charged reduce the freezing temperature. Accordingly, droplets of water cooled down on a negatively charged LiTaO₃ surface and remaining liquid at -11°C freeze immediately when this surface is heated to -8°C, as a result of the replacement of the negative surface charge by a positive one. Furthermore, powder x-ray diffraction studies demonstrated that the freezing on the positively charged surface starts at the solid/water interface, whereas on a negatively charged surface, ice nucleation starts at the air/water interface.

The chemical strain effect in solids is the deviation from linear elasticity due to the association and dissociation of point defects. Although to date this effect has been observed and studied only in Ce_0.8Gd _0.2O_1,9, one may expect that it will be found in other ionic and mixed conductors containing a large concentration of point defects. In this work, some practical applications of materials exhibiting the chemical strain effect are discussed. Based on the example of Ce_0.8Gd _0.2O_1,9, mechanical structures built from these materials should exhibit exceptional mechanical stability and are therefore very attractive for use as components of solid oxide fuel cells (SOFC) or other devices subjected to large and frequent temperature variations. The ability of these materials to withstand large strain without accumulating large stress also makes them potentially useful as flexible elements in micro-electromechanical systems (MEMS).

Nonthermal crystallization of amorphous barium titanate (BTO) was initiated by a monochromatic x-ray microbeam from a synchrotron radiation source. Following x-ray exposure, micron-sized BTO single crystals with a true square pyramid shape appeared on the surface of an amorphous BTO substrate-free film. The location and size of the areas in which crystal growth appeared fit well the x-ray microbeam path and size, respectively. A plausible mechanism of x-ray induced initiation of nonthermal crystallization in BTO is proposed. The observed phenomenon holds promise for materials engineering at nanoscale and crystallization of amorphous materials in situations where heating must be avoided.

Photon up-conversion (UC) and photon-induced multiple-exciton generation (MEG) are proposed directions that are of increasing interest for improving photovoltaic (PV) conversion efficiencies via "photon (or light) management". Straightforward analysis of these approaches for non-concentrated single-junction cells in the detailed balance limit yields a theoretical PV conversion limit of 49%, instead of 31% without UC and MEG. With what we estimate to be optimistic, maximal realistic efficiencies (25% for UC; 70% for MEG) this limit becomes

Dense CeO₂ layers of 350 nm thickness, with columnar grains of size 25 nm, were RF-sputtered on silicon. ¹⁸O isotope exchange in the temperature range from 200 to 575 °C showed surface exchange at CeO₂ as the rate-determining step, while diffusion through the polycrystalline thin layer was fast. The surface exchange coefficients controlled by surface or grain boundary processes were found to be k_s = 2.7 × 10^{- 8} exp (frac(- 0.3 eV, k T)) cm s^{- 1} or k_gb = 1 × 10^{- 9} exp (frac(- 0.3 eV, k T)) cm s^{- 1}. Comparison with literature data on doped ceria revealed that surface exchange could be dominated by grain boundary processes. A lower limit for the diffusion coefficient was determined as 10^{- 15} cm² s^{- 1} at 575 °C.

The influence of the Ti/Ba ratio on the formation of pyroelectric and piezoelectric quasi-amorphous BaTiO₃ films was investigated. Three types of films, Ti-rich, Ba-rich, and stoichiometric, were pulled through a temperature gradient or subjected to isothermal heating. The quasi-amorphous polar phase only formed in films pulled through the temperature gradient with Ti/Ba ratio within the broad range of 0.95-1.1. This implies that quasi-amorphous pyroelectric and piezoelectric thin films are significantly more tolerant of a deviation from stoichiometry than their crystalline counterparts.

Amorphous piezo and pyroelectric phases of BaZr₃ and SrTiO ₃ can form quasiamorphous phases although neither of them have a polar crystalline polymorph. Amorphous films of SrTiO₃ or BaZrO ₃ (50- 200 nm thick) were deposited by radiofrequency magnetron sputtering on highly conductive Si substrates. The as-deposited amorphous films were then pulled through a temperature gradient in order to induce a strong inhomogeneous stress that could align the local bonding units. Stoichiometry of all samples was verified with X-ray photoelectron spectroscopy before and after heat treatment. These findings are the first instance of successful manipulation of local bonding units to obtain a noncrystalline inorganic solid with desired properties. Though qualitative, this method is highly reliable because the influences of electrical interferences, friction-induced electricity, and electrostriction can easily be excluded.

Two mechanisms by which an inorganic thin film may reversibly adapt to externally imposed strain have been considered: (1) the chemical strain effect and (2) self-organization of polycrystalline macro-domains. The chemical strain effect is due to the transformation of the elastic energy of an externally applied stress into chemical energy of interacting point defects. This effect may be observed in solids with a large concentration of interacting point defects if the interaction is accompanied by a large change in specific volume. Self-organization of polycrystalline macro-domains may take place when single-domain ferroelastic grains minimize intergrain strain via approximate mutual alignment of their crystallographic axes. Each such macro-domain region has a preferred size and direction of alignment. In the presence of externally applied stress, these regions may reorganize, thereby partially converting the elastic energy of the external stress into the elastic energy of intergrain stress. Although very different in nature, both mechanisms result in reversible strain-relaxation. The conditions under which each of these effects may be present are understood well enough to provide clear guidance for preparation of materials and for their incorporation into practical devices.

A method and device are presented for measuring the electrical properties of a specimen. The specimen is excited with high energy radiation to cause emission of internal charged particles from the specimen. Electrical power is supplied to a circuit, that is formed by the specimen and any added component connected to a back contact of the specimen. The electric power supply includes at least one of the following: irradiating the circuit with low energy charged particles; subjecting the circuit to an external field of the kind affecting the flux of emitted internal charged particles, and supplying a bias voltage to the back contact of the specimen. During the power supply to the specimen, at least one of the following is carried out: an electric current through the specimen is measured, and the emitted charged particles are analyzed versus their energy (using a contactless voltmeter) which provides local potential values at chemical entities of the specimen. This technique enables determination of rich, chemically resolved, electrical properties of a specimen, such as IV characteristic, and/or evaluation of a work function characteristic, and/or characterization of electric leakage or breakdown conditions of the sample, and/or characterization of accumulation of charge within at least one region of the sample, and/or chemically resolved photovoltaic characteristics (photovoltage and/or photocurrent) of the sample.

The formation of polycrystalline macro-domains by self-organization of ferroelectric grains was studied. It was observed that if the phase transformation is accompanied by lowering the crystal symmetry and the product phase forms variants with different orientations with different self-strain. Incase of polycrystals the formation of polydomains was observed with transformation of grains. The issues related to formation of interactions between the convex and concave sides of a bent crystals were also discussed.

The thermal stability of amorphous ionic solids is usually attributed to kinetic considerations related to masstransport. However, there are a number of amorphous ionic solids, which have recently been described, whose unusual resistance to nucleation and subsequent crystallization cannot be explained by mass transport limitations. Examples have been found in a large variety of fields, spanning the range from thin solid films to biomineralization. This poses a question regarding a possible common mechanism for the stabilization of amorphous ionic solids. Here we present a model which explains the formation and thermal stability of quasi-amorphous thin films of BaTiO₃, one of the amorphous systems recently described which exhibit unusual thermal stability. On the basis of the experimental evidence presented we suggest that nucleation of the crystalline phase can occur only if the amorphous phase undergoes volume expansion upon heating and transforms into an intermediate low density amorphous phase. If volume expansion is unobstructed by external mechanical constraints, nucleation proceeds freely. However, thin films are clamped by a substrate; therefore, volume expansion is restricted and the low-density intermediate phase is not formed. As a result, under certain conditions, nucleation may be completely suppressed and the phase which appears is quasi-amorphous. A quasi-amorphous film is under compressive stress and as long as the mechanical constraints are in place it remains stable at the temperatures that normally lead to crystallization of amorphous BaTiO ₃. Quasiamorphous thin films of BaTiO₃ exhibit pyroelectricity, the origin of which is also explained by the proposed model.

Cerium oxide is stable to commonly used aqueous etching agents and can be reliably etched only by a combination of chlorine and fluorine plasma. This hinders practical applications of pure and doped ceria thin films in bulk and surface micromachining. In the present work, the reasons for the chemical stability of cerium oxide in aqueous media were analyzed and two etching solutions were investigated. In the absence of stirring, the etching rate dropped with time. In an ultrasonic bath, etching was isotropic with a constant rate of ∼10 nm/min. This permits patterning of ceria films using chromium as a mask and demonstrates practical applicability of the proposed etching solutions.

The modeling of distribution of mobile charge carriers in the space-charge regions at grain boundaries of ceramic materials was done. The standard free chemical potentials of the defects were set to be constant in accordance with the space-charge model. The modeling predicted that a contact of two grains that differed only in size, led to a redistribution of mobile ions between grains.

Ion beam sputtering of chemical compounds is in general nonstoichiometric. The problem is especially severe for inorganic insulators because target charging and ionic emission render sputtering rates unstable. This study reports on the influence of target charging on ion beam sputtering of Al ₂O ₃ and LiNbO ₃ films on Si and Al ₂O ₃/Si substrates. It was found that undesirable ionic emission could be minimized by eliminating target charging, controlled via electron to ion neutralization ratio of the incident beam. Experimental data suggest that the stoichiometric sputtering corresponds to zero target charging and thus can be used as an effective feedback parameter during deposition. When the target charging was minimal, high quality stoichiometric Al ₂O ₃ films were obtained without the need for oxygen supplied to the deposition chamber. The dependence of refractive index, residual stress, and specific resistance on neutralization ratio showed abrupt change in the vicinity of zero target charging. In a separate experiment, minimization of the target charging helped to maintain stoichiometry during ion beam sputtering of LiNbO ₃, suggesting that this method is also beneficial for sputtering of ternary compounds.

We investigated mechanical stress in thin freestanding BaTiO₃ films prepared on bare silicon and on silicon, covered by a 120 nm thick, randomly oriented Al₂O₃ buffer. Films prepared on bare silicon by RF sputtering are essentially stress-free. However, they disintegrate after substrate removal. In contrast, the films prepared on the Al₂O₃ buffer have high tensile stress, but retain their structural integrity after separation from the substrate. Substrate removal is accompanied by film corrugation; at the same time, the freestanding films resonate mechanically. This seeming contradiction can be understood on the basis of a recently developed theory of 2D clamping in thin ferroelectric films.

We show that percolation can control not only diffusion in solids, but in the case of semiconductors also their electrical activity, via the doping action of the diffusing species. This occurs in (Hg1-xCdx)Te (MCT) when x(Cd)