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A-T-Al aluminides (where A = actinide/lanthanide/rare earth elements and T=transition metal) were intensively studied due to their ability to form heavy fermion compounds that could possess unique physical properties [1-3, for example]. Although A-T-Al family contains hundreds of phases, they can be classified into only a few series of phases with isotypical structures. Al richest are: tetragonal ATxAl12-x (ThMn12 type), tetragonal AT2Al10 (CaCr2Al10 type), orthorhombic AT2Al10 (YbFe2Al10 type) and cubic AT2Al20 (CeCr2Al20 type). Due to the intimate link between structure and properties, in order to understand and enhance physical properties – exact atomic structure of these materials should be known. Such researches are performed usually using “trial and error” approach, e.g. cast and characterize, which could be time consuming. It would be of clear benefit to formulate a rule that could predict the relative stability of the structures that may form in the ternary Al-richest phases in the A-T-Al systems.
Current research was conducted with an aim to understand the influence of A and T atom types on the formation of the stable structures in the AT2Al20 alloys. The work was performed systematically, investigating several AT2Al20 alloys both experimentally and by Density Functional theory (DFT) calculations. Study on the ThT2Al20 systems (where T=Ti, V, Cr, Mn and Fe) was previously performed by our group suggesting that the magnetic moment of T atoms can be used as a good descriptor of phase stability [4-5]. Now, we focus on the investigation of the AMn2Al20, where A elements were selected according to their electronic structure. Theoretical and experimental results were found to be in perfect agreement. By analyzing the density of states (DOS) we found that the different behavior of the 4f and 5f-shell electrons of the heavy atom, eventually determines which structure will be favorable [6].
While studying these A-T-Al systems new unknown ternary phases were discovered: Th2Ni10Al15 [7] and Nd2Re3Al15. Since in both cases the alloys of an interest did not attain equilibrium state despite the prolonged heat treatments - they contained multiple phases. Therefore, electron crystallography methods were the only viable tool applicable for structure solution of these phases. In current research, electron diffraction tomography (EDT) approach was successfully used for solution of atomic structure of both phases.