Abstract
A-T-Al aluminides, where A = actinide, lanthanide or rare earth elements and T=transition metals, have attracted considerable attention as potential materials where heavy fermions may be formed. This led to the discovery of superconducting properties in cubic AT2Al20 compounds with CeCr2Al20-type crystal structure. Other Al-rich aluminides, belonging to these A-T-Al systems, exhibited different physical properties as a function of their crystal structure. Thus, predicting the stable structure of the Al-richest phase that will form in the A-T-Al systems is highly valuable. Stability of the crystal structures, forming in the CeT2Al20 and YRe2Al20 systems, was studied in current research using density functional theory (DFT) calculations. It is demonstrated that the total spin magnetic moment of the transition metal can be used as a descriptor for phase stability assessment in the AT2Al20 systems, where T is a 5d transition metal. Basing on crystallographic considerations, degree of distortion of the coordination polyhedrons, formed around T atoms, can be directly connected to the specific type of structure crystallizing in these systems.
Highlights
A-T-Al family of alloys was extensively studied, due to its ability to form heavy fermions [1,2,3,4,5,6,7,8,9,10,11,12]
There are hundreds of possible ternary Al-rich A-T-Al phases which can form in these systems, but in reality all these phases can be classified into only a handful of structure types, such as tetragonal ATx Al12-x (ThMn12 type) [4,13], tetragonal AT2 Al10 (CaCr2 Al10 type) [14], orthorhombic AT2 Al10 (YbFe2 Al10 type) [15] and cubic AT2 Al20 (CeCr2 Al20 type) [16], see Table 1
Ce with electron configuration of [Xe]4f1 5d1 6s2 was chosen as representative of the A atom type in the studied AT2 Al20 composition and the 5d transition metals changed from Ta to Re
Summary
There are hundreds of possible ternary Al-rich A-T-Al phases which can form in these systems, but in reality all these phases can be classified into only a handful of structure types, such as tetragonal ATx Al12-x (ThMn12 type) [4,13], tetragonal AT2 Al10 (CaCr2 Al10 type) [14], orthorhombic AT2 Al10 (YbFe2 Al10 type) [15] and cubic AT2 Al20 (CeCr2 Al20 type) [16], see Table 1. The amount of possible structures forming in these systems is even less than listed here since tetragonal AT2 Al10 (CaCr2 Al10 type) and orthorhombic AT2 Al10. The unit cell of the AT2 Al20 structure (CeCr2 Al20 -type) may be presented as a packing of coordination polyhedrons formed around heavy atoms. Such polyhedron is of Frank-Kasper type [20]
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