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In the current work we have studied the crystallographic relationship between the AT2Al10 phases (where A = actinide, lanthanide and rare earth element and T = transition metal). It is known that with this stoichiometry two structure types exist: tetragonal CaCr2Al10 and orthorhombic YbFe2Al10. It was found that both CaCr2Al10 and YbFe2Al10 types are structural derivatives of the ThMn12 type structure (which has more general formula of ATxAl12−x, with x > 2). CaCr2Al10 structure has a group-subgroup relationship with the ThMn12 structure, while the relationship of the YbFe2Al10 to the ThMn12 was proved applying the strong reflection approach, suggested initially for approximants of quasi-crystals. Proposed here relationship between the studied structures explains the small difference in total energies, calculated using Density Functional Theory. Understanding the connection between these phases allows regarding AT2Al10 composition as somewhat extension of the ATxAl12−x compositional range. Due to the unique magnetic properties of the ATxAl12−x phases, tunable as a function of crystallographic structure, study of structural stability and crystallographic relationships of related phases are of outmost importance. [ABSTRACT FROM AUTHOR]

A-T-Al family of alloys (where A = actinides, lanthanides or rare earth elements; T = transitional metals) has unique physical properties. AT 2 Al 20 phases are of particular importance since they have exhibited superconductivity properties. Understanding the reasons for the formation of the AT 2 Al 20 structures in various A-T-Al alloys is the objective of current study, since it will allow formulation of rule for prediction of stable structures in these alloys. Such rule will shorten the research time because usually the search for these phases (although is based on some criteria) performed by serendipity. Formerly we proposed that type of transition metal dictates the symmetry of the ternary phases' structure formed in the AT 2 Al 20 systems, while symmetry breakage point was found to be in T = Mn. Here, AMn 2 Al 20 alloys were studied with a purpose to understand the influence of A type atoms on the stable ternary aluminide formed. Despite adequate amount of Al provided in these alloys, cubic AMn 2 Al 20 phase did not formed in any of the studied compounds besides A = U. The results of Density Functional Theory calculations were in excellent agreement with the experimental ones. It was found that proposed earlier rule for the prediction of the stable structure in these systems using the minimal magnetic moment of the transition metal works as long as A type atoms do not have 5 f -electrons. Otherwise, the stable structure in these systems can be assessed by the minimal average energy of the transitional metal 3 d -electrons participating in bonding. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]