Why UFe xAl 12− x phase does not crystallize with ThMn 12-structure type, when x = 2?

Abstract

The crystallographic structure of recently reported orthorhombic UFe 2Al 10 phase, which belongs to the YbFe 2Al 10-structure type is different from the well known tetragonal UFe x Al 12− x (3 < x < 8) having ThMn 12-structure type. Comparative Density Functional Theory (DFT) study of the relative stability of the orthorhombic UFe 2Al 10 phase with respect to different models of tetragonal ThMn 12-type structures with the same composition is carried out to explain this unusual phenomenon. It is shown that the fine interplay between the overlapping of 3d-states of Fe and 5f-states of U in the region −2.5 ÷ −0.3 eV below the Fermi energy dictates the lower total energy of orthorhombic UFe 2Al 10 phase in comparison with tetragonal UFe 2Al 10 phase crystallized in ThMn 12 structure. On the example of UFe 2Al 10 it is also directly demonstrated that DFT calculations in the framework of the Full Potential + Linear Augmented Plane Wave method within the local density approximation may be used for refining the structure of complicate compounds. The calculated equilibrium volume, lattice parameters and atomic Wyckoff positions of UFe 2Al 10 intermetallic compound are in very good agreement with experimental data.