Publications

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.

Raman spectroscopy is applied for non-destructive characterization of strain in crystalline thin films. The analysis makes use of the numerical value of the mode Gruneisen parameter gamma, which relates the fractional change in the frequency of a Raman-active vibrational mode and the strain-induced fractional change in the unit cell volume. When in-plane, compressive biaxial strain in aliovalent doped CeO₂-films is relieved by partial substrate removal, the films exhibit values of gamma for the F_2g vibrational mode which are similar to 30% of the literature values for bulk ceramics under isostatic stress. This discrepancy has been attributed to a negative contribution from the anelastic (time-dependent) mechanical properties of aliovalent-doped ceria. Here we propose a way to "separate" anelastic and elastic contributions to the F_2g mode Gruneisen parameter. Mechanically elastic yttria (Y₂O₃) films on Ti/SiO2/Si substrate serve as "control". The values of gamma calculated from the change in frequency of the similar to ∼375 cm^-1 F_2g Raman-active mode are close to the literature values for bulk yttria under isostatic stress. This work should serve to provide a protocol for characterization of selective sensitivity to different strain components of doped ceria thin films.

This work reports that the octahedral hydrated Al³⁺ and Mg²⁺ ions operate within electrolytic cells as kosmotropic (long-range order-making) “ice makers” 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 “ice-like” 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 “electro-chemo-mechanical (ECM) effect” 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 TiOx/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 TiOx 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 VOx/20GDC. Electrical characterization suggests that the formation of several coexisting VOx nano-oxide phases is responsible for the longer response times as compared to TiOx/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.
•nanocrystalline composites of V-, Nb-, Mo-, Cu- and Ag-oxide/20GDC were prepared.•structure, crystal phase, oxidation state, composition and ECM functionality examined.•V-based composite was shown to be suitable for ECM actuation.•composition of the nanocomposite corresponds to VOx/20GDC.

Sulfur dioxide in flue gas from coal-fired power plants presents both ecological and health hazards. Scrubbing dilute, sulfurous flue gas with carbonate eutectic melt at 823K can mitigate these hazards, but for an efficient and economical process, the melt must be regenerated and any resulting contaminants, in particular carbonyl sulfide gas (COS), a known neurotoxin, eliminated. In order to characterize this final stage in the recycling process, the thermal decomposition of COS was studied. A laboratory-scale, quartz flow reactor operating in the temperature range 773–1123 K was selected, with the optional addition of one of three potential catalysts to promote decomposition: an untreated or aqua regia-treated catalytic convertor, γ-alumina powder and charcoal. The extent of decomposition and the reaction products were monitored via gas chromatography as a function of reactor temperature and gas residence time. The feed gas concentration of COS was generally held constant at 30 mol%, the remainder being N2. Under the conditions of our study, 7–44 min residence time, catalytic effects on the kinetics of the COS decomposition reaction were not observed. AddingCO2, thereby lowering the feed COS concentration to 20 mol%, resulted in increased COS decomposition for T

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

The technologically important frequency range for the application of electrostrictors and piezoelectrics is tens of Hz to tens of kHz. Sm3+- and Gd3+-doped ceria ceramics, excellent intermediate-temperature ion conductors, have been shown to exhibit very large electrostriction below 1 Hz. Why this is so is still not understood. While optimal design of ceria-based devices requires an in-depth understanding of their mechanical and electromechanical properties, systematic investigation of the influence of dopant size on frequency response is lacking. In this report, the mechanical and electromechanical properties of dense ceria ceramics doped with trivalent lanthanides (RE0.1Ce0.9O1.95, RE = Lu, Yb, Er, Gd, Sm, and Nd) were investigated. Young’s, shear, and bulk moduli were obtained from ultrasound pulse echo measurements. Nanoindentation measurements revealed room-temperature creep in all samples as well as the dependence of Young’s modulus on the unloading rate. Both are evidence for viscoelastic behavior, in this case anelasticity. For all samples, within the frequency range f = 0.15–150 Hz and electric field E ≤ 0.7 MV/m, the longitudinal electrostriction strain coefficient (|M33|) was 102 to 104-fold larger than expected for classical (Newnham) electrostrictors. However, electrostrictive strain in Er-, Gd-, Sm-, and Nd-doped ceramics exhibited marked frequency relaxation, with the Debye-type characteristic relaxation time τ ≤ 1 s, while for the smallest dopants—Lu and Yb—little change in electrostrictive strain was detected over the complete frequency range studied. We find that only the small, less-studied dopants continue to produce useable electrostrictive strain at the higher frequencies. We suggest that this striking difference in frequency response may be explained by postulating that introduction of a dopant induces two types of polarizable elastic dipoles and that the dopant size determines which of the two will be dominant.

Characterization of the ionic transport and corresponding electro-elastic deformations in cerium oxide at the nanoscale are important for the understanding of the mechanism of the local response under an external electric field, especially the mechanisms of the 'non-Newnham''-Type giant electrostriction. Here, we introduce a methodological approach to the analysis of signals in the piezoresponse force microscopy/electrochemical strain microscopy allowing decoupling ionic motion, electrostriction, and electrostatic contributions to the electromechanical signals based on a precise analysis of the electromechanical amplitude and phase as a function of temperature, and AC and DC biases. The ionic motion was demonstrated to be hampered in a 30-300°C temperature range, the typical operational range of commercial SPM microscopes. The local electromechanical response was interpreted as a mixture of the electrostatic-force-meditated response and conventional electrostriction.

Electromechanically active ceramic materials, piezoelectrics and electrostrictors, provide the backbone of a variety of consumer technologies. Gd- and Sm- doped ceria are ion conducting ceramics, finding application in fuel cells, oxygen sensors and, potentially, as memristor materials. While optimal design of ceria-based devices requires thorough understanding of their mechanical and electro-mechanical properties, reports of systematic study of the effect of dopant concentration on the electromechanical behavior of ceria-based ceramics are lacking. Here we report the longitudinal electrostriction strain coefficient (M33) of dense RExCe(1-x)O(2-x/2) (x≤0.25) ceramic pellets , where RE=Gd or Sm, measured under ambient conditions as a function of dopant concentration within the frequency range f=0.15-350 Hz, electric field amplitude E≤0.5 MV/m. For >100 Hz , all ceramic pellets tested, independent of dopant concentration, exhibit longitudinal electrostriction strain coefficient with magnitude on the order of 10-18 m2/V2. The quasi-static (f

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.

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.

We have developed a simple method for depositing high quality platinum (Pt) metal contacts without the necessity of placing the substrate in vacuum or heating it above 180 °C. This method is particularly beneficial for hydrated oxide ceramics, as it prevents water loss and subsequent conductivity degradation. A mixture of two organic solvents was used: ethylene glycol monoethyl ether (EEE) and acetone. By dispersing the precursor PtCl
₄ in this mixed non-volatile/volatile solvent, homogeneous drying patterns were achieved. EEE was used as the reducing agent, providing a relatively slow rate of Pt deposition, and thereby avoiding formation and subsequent coagulation of Pt clusters. Drop casting of the solution (25 μL/cm
²) on mirror-polished surfaces was performed at 25 °C followed by 5 min partial solvent evaporation. The substrate was then heated to 180 °C for ~30 s, resulting in the formation of a metallic Pt layer. The method was successfully tested on 5 mol% Y doped BaZrO
₃ and 10 mol% Gd doped ceria ceramic pellets, alumina plates, and Kapton ® polymer sheets. The in-plane sheet resistance was 30–110 Ω at room temperature after a single deposition cycle. Because of its versatility and low cost per deposition, the proposed method is very promising for a variety of substrates where high quality electrical contacts prepared at low temperature are required.

Although Pb Halide perovskites (HaPs) can be prepared as organic electronic materials, they resemble top-quality inorganic semiconductors, especially with respect to their low defect densities, as derived from optical and electronic transport studies. Among causes for such low defect densities were 'defecttolerance' (proposed) and 'self-healing' (experimentally identified). We show that HaPs are likely an example of a class of materials that cannot support static bulk defect densities significantly above thermodynamically-dictated densities. The reasons are (a) the free energy to form HaPs (from binary halides) is less than the formation energies of (static) defects in them and (b) the small kinetic stabilization of such defects. We summarize the evidence for such a situation and conclude that higher defect densities in polycrystalline films likely result from the (expected) smaller defect formation energy at surfaces and grain boundaries than in the bulk. This situation directly limits the options for doping such materials, and leads to the counter-intuitive conclusion that a low free energy of formation (from the binaries) can lead to self-healing and, consequently, to low densities of static defects, to be distinguished from dynamic ones. The latter can be benign in terms of (opto)electronic performance, because of their relatively short lifetimes. We propose that the conditions that we formulated can serve as search criteria for other low defect density materials, which can be of interest and beneficial, also for applications beyond optoelectronics.

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.

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.

Gd‐doped ceria (CGO), one of the most extensively studied oxygen ion conductors, is a low dielectric constant/low mechanical compliance material exhibiting large nonclassical electrostriction. The electromechanical response of the micro‐electromechanical devices with CGO films as an active material described previously can not be attributed exclusively to electrostriction. Here it is shown that, below 1 Hz, in addition to electrostriction (second‐harmonic response), there is a strong contribution of the electro‐chemomechanical effect (ECM, first harmonic response). ECM is the change in mechanical dimensions of ionic and mixed ionic‐electronic conductors as a result of a change in chemical composition induced by an electric field. In batteries, the presence of ECM is highly detrimental. In ceria at room temperature, it was considered to be negligible because of slow oxygen diffusion. This work demonstrates ECM actuation at ambient temperature and moderate electric field (

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

The magnetic properties of undoped, bulk CeO2 are not fully understood. In contrast to nanocrystalline ceria that exhibits paramagnetism attributed to Ce3+ at grain surfaces, bulk ceria is weakly paramagnetic, despite the absence of magnetic ions. In the present work, the magnetic susceptibility of bulk ceria ceramics doped with Lu3+, which has neither spin nor orbital angular momentum, was measured in order to assess the relative contributions of the crystal lattice, residual Ce3+ and oxygen vacancies to the overall bulk magnetization. We observed a magnetic response consisting of two parts: temperature independent (5-300 K) magnetic susceptibility, and Curie-Weiss paramagnetism. The temperature independent susceptibility decreases linearly with Lu content, and becomes diamagnetic at 30 mol% Lu. The Curie-Weiss magnetism visible at low temperatures was identified as resulting from a few ppm of Fe contaminant. However, Fe contamination does not contribute to the temperature independent paramagnetism. No contribution from Ce3+ could be detected. The fact that the magnetization decreases with Lu content, even though the concentration of oxygen vacancies, and the lattice defects associated with them, increases, indicates that neither is coupled to the magnetic field. Weak, temperature-independent paramagnetism in non-metals is usually attributed to a second order, Van Vleck-type magnetization. However, Van Vleck paramagnetism requires that the population of the first excited state be constant within the range of temperatures investigated. We discuss possible modifications of the large band gap electronic structure of undoped ceria which could account for our observations.

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.

Micro-Raman spectroscopy and X-ray diffraction were used to study time-dependent structural changes in sputtered Ce_1-xGd_xO_2-x/2 films. The F_2g peak position was measured at five well-defined film locations; X-ray diffraction assessed in-plane compressive strain and unit cell volume. For x = 0.05, at all locations monitored post-annealing, the F_2g frequency continued to increase during two weeks and for x = 0.10, at 4 of 5 locations during six weeks. This time-dependent behavior is attributed to relaxation of local elastic dipolar strain fields. Raman spectroscopy can properly evaluate strain in thin films of these materials only when mechanical properties, defect structure, temporal and thermal history are considered.

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.

Materials are central to our way of life and future. Energy and materials as resources are connected, and the obvious connections between them are the energy cost of materials and the materials cost of energy. For both of these, resilience of the materials is critical; thus, a major goal of future chemistry should be to find materials for energy that can last longer, that is, design principles for self-repair in these.

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.

To experimentally (dis)prove ferroelectric effects on the properties of lead-halide perovskites and of solar cells, based on them, we used second-harmonic-generation spectroscopy and the periodic temperature change (Chynoweth) technique to detect the polar nature of methylammonium lead bromide (MAPbBr₃). We find that MAPbBr₃ is probably centrosymmetric and definitely non-polar; thus, it cannot be ferroelectric. Whenever pyroelectric-like signals were detected, they could be shown to be due to trapped charges, likely at the interface between the metal electrode and the MAPbBr₃ semiconductor. These results indicate that the ferroelectric effects do not affect steady-state performance of MAPbBr₃ solar cells.

The impact of ⁶⁰Co gamma-irradiation on n-channel AlGaN/GaN high-electron-mobility transistors was studied by means of temperature-dependent electron beam-induced current (EBIC) and cathodoluminescence (CL) techniques. For the doses up to ∼250 Gy, an enhancement of minority carrier transport was observed as evident from the EBIC measurements. This enhancement is associated with internal electron irradiation induced by the primary gamma photons. For the doses above ∼250 Gy, deterioration in minority carrier transport was explained by carrier scattering on radiation-induced defects. It is shown that calculated activation energy from the EBIC and CL measurements follows exactly the same trend, which implies that the same underlying phenomenon is responsible for observed findings.

The validity and limitations of two quantitative approaches for estimating the height of the potential barrier at grain boundaries, Ψ_gb, in polycrystalline ionic conductors are examined both theoretically and experimentally. The linear diffusion model recently proposed by Kim and Lubomirsky determines Ψ_gb from the value of the power exponent of the current (I_gb)-voltage (U_gb) relationship at the grain boundary, dln(I_gb)/dln(U_gb), while the conventional approach calculates Ψ_gb from the ratio of the grain boundary resistivity to the grain core resistivity. The results of our theoretical analysis demonstrate that both approaches should yield consistent values for Ψ_gb if the ionic current through the grain boundary is limited exclusively by space charge. While the value of Ψ_gb obtained by the power law procedure is relatively insensitive to other causes of current obstruction, e.g. current constriction and/or local structural disorder, the resistivity ratio method, if not explicitly corrected for these additional limitations, results in a considerable overestimate of the grain boundary potential barrier. Hence, it is possible to distinguish between grain boundary resistance due to the presence of space charge and that due to additional sources by comparing the values of Ψ_gb determined using each of the two methods. Our theoretical analysis is confirmed experimentally with 3 mol% Gd-doped ceria with and without an additional source of current constriction across the grain boundary.

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.

The conclusions reached by a diverse group of scientists who attended an intense 2-day workshop on hybrid organic-inorganic perovskites are presented, including their thoughts on the most burning fundamental and practical questions regarding this unique class of materials, and their suggestions on various approaches to resolve these issues.

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.

The paper encompasses the investigation of the effective pyroelectric behavior of materials in different structures/systems such as the bimorphs and the sandwiched structure, with the variation of the temperature. Different mathematical approaches have been used to include the secondary factors contributing to the effective pyroelectric coefficient, and it has been included to obtain a consolidated expression of the same. The effective pyroelectric coefficient for few selected ferroelectric materials has been deduced using their actual physical constants to get a closer resemblance with the practical device. This paper would be a step forward to the fabrication of layered material with a higher pyroelectric coefficient for a possible energy harvesting applications also.

Display of pyroelectricity along nonpolar directions of crystals or from surfaces implies structural disorder or presence of polar surface layers. Nonpolar {210} faces of polar dl-alanine crystals display far larger pyroelectric effect than that at the polar {001} faces. Similarly, pyroelectricity is reported from {110} faces of centrosymmetric crystals of dl-aspartic acid. The origin of the disorder is due to an interchange of enantiomers at specific chiral crystal sites as supported by atom-atom potential energy computations and by pyroelectric effect observed on the nonpolar crystals of l-alanine intentionally doped with opposite enantiomers. These results should explain the riddle of the needle-like morphology of dl-alanine. The {100} faces of dl-serine and the {021} faces of dl-glutamic acid monohydrate crystals exhibit pyroelectricity due to surface wetting, whereas pyroelectricity originating from the {210} faces of enantiomerically doped l-alanine crystals could be deciphered as arising both from surface wetting and enantiomeric bulk disorder.

XRD measurement of the room temperature in-plane and out-of-plane d-spacings of the (422) diffraction peak of 11 thin film samples of fluorite Ce_0.8Gd_0.2O_1.9 demonstrates that the zz and xx (=yy) components of the strain tensor for this material are not related via a constant, i.e. the Poisson ratio, as is the case for elastic materials. Rather, these strains are independent. We attribute this behavior to the inelastic character of Ce_0.8Gd_0.2O_1.9 deriving from the chemical strain effect, i.e. the lability of point defect-containing complexes under stress. Chemical strain is dependent on the thermal and mechanical history of the film, and above 200 C, is no longer observed, being transformed into elastic strain and stress. This transformation may compromise the mechanical stability of Ce_0.8Gd_0.2O_1.9 containing devices, which must operate over a broad temperature range. Measurements analogous to those described here can assist in predicting the magnitude of such an effect.

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 mu m 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

Measurements of the elastic modulus of pure and doped ceria are summarized from the literature and analyzed with a view towards understanding the experimentally established dependence on temperature, doping level and oxygen vacancy concentration. At least two chemical properties affect the elastic modulus of pure and doped ceria: (i) the presence of vacancies decreases the strength of the chemical bonds; and (ii) low-temperature adaptation of the fluorite structure to the presence of oxygen vacancies is accompanied by an increase in unit cell volume.

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).

The kinetics of point-defect association/dissociation reactions in Ce _0.8Cd_0.2O_1.9 and their influence on the crystal lattice parameter are investigated by monitoring thermally induced stress and strain in substrate and self-supported thin films. It is found that, in the temperature range of 100-180 °C, the lattice parameter of the substrate-supported films and the lateral dimensions of annealed, self-supported films both exhibit a hysteretic behavior consistent with dissociation/ association of oxygen vacancy-aliovalent dopant complexes. This leads to strong deviation from linear elastic behavior, denoted in the authors' previous work as the "chemical strain" effect. At room temperature, the equilibrium state of the point defects is reached within a few months. During this period, the lattice parameter of the substrate-supported films spontaneously increases, while the self-supported films are observed to transform from the flat to the buckled state, indicating that formation of the dopant-vacancy complex is associated with a volume increase. The unexpectedly slow kinetics of establishing the defect equilibrium at room temperature can explain the fact that, depending on the sample history, the "observable" lattice parameters of Ce_0.8Cd_0.2O_1.9, as reported in the literature, may differ from one another by a few tenths of a percent. These findings strongly suggest that the lattice parameter of the materials with a large concentration of interacting point defects is a strong function of time and material preparation route.

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

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.

Self-supported films of nanocrystalline BaTi O3 exhibit a two orders of magnitude enhancement of the pyroelectric coefficient (≈1 μC cm2 K) with respect to the value measured for a single BaTi O3 crystal. The enhancement strongly depends on film geometry and appears only in buckled films where ferroelectric grains undergo self-organization into polycrystalline macrodomains. The authors posit that the enhancement of the pyroelectric effect is related to 90° polarization switching and is, therefore, similar in nature to an "extrinsic" piezoelectric effect.

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 I–V 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 mass transport. 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 BaTiO3. Quasi-amorphous 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.

We show that substrate-free crystallized barium titanate (BaTiO3) films adopt a hexagonal structure, whereas substrate-supported films assume the commonly observed tetragonal phase. However, in contrast to the known hexagonal BaTiO3, the substrate-free crystallized films demonstrate a small but measurable pyroelectric effect, and do not exhibit phase transitions in the 25-423 K temperature range. Thus the substrate-free crystallized BaTiO3 represents a heretofore unreported crystallographic modification of BaTiO3. (C) 2002 American Institute of Physics.

We created a material with a composition gradient within each grain. Due to the graded composition the ceramic does not show a sharp change in dielectric constant near the relaxation frequency. Instead, we observe gradual decrease in dielectric constant with frequency, with the loss tangent remaining practically unchanged (below 0.02 everywhere within the frequency range 0.0003-3 GHz). The tunability of the ceramic decreases with increasing frequency but remains in the order of 10% at 3 GHz. Thus we conclude that the dielectric relaxation in high purity (Ba,Sr)TiO₃ occurs predominantly by Ti⁴⁺ ion hopping relaxation. We also expect that the concept of intragrain concentration gradient ceramics may become a useful material for a wide range of electronic devices. PACS: 77.22.Gm, 77.22.Ch, 77.84.Dy

Substrate-free crystallization of BaTiO₃ thin films was investigated. It was found that the substrate-free crystallized BaTiO₃ films attain a hexagonal structure, whereas the substrate-supported films always crystallize in the tetragonal phase. The substrate-free crystallized hexagonal BaTiO₃ demonstrates detectable pyroelectric effect and does not exhibit phase transitions in the 25-423 K temperature range. Therefore, the substrate-free crystallized BaTiO₃ represents a previously unreported phase of BaTiO₃.

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)