Lattice anisotropy in uranium ternary compounds: UTX

Several U-based intermetallic compounds (UCoGe, UNiGe with the TiNiSi structure type and UNiAl with the ZrNiAl structure type) and their hydrides were studied from the point of view of compressibility and thermal expansion. Confronted with existing data for the compounds with the ZrNiAl structure type a common pattern emerges. The direction of the U–U bonds with participation of the 5f states is distinctly the “soft” crystallographic direction, exhibiting also the highest coefficient of linear thermal expansion. The finding leads to an apparent paradox: the closer the U atoms are together in a particular direction the better they can be additionally compressed together by applied hydrostatic pressure.

► Compressibility and thermal expansion of several U-based compounds were established.
► The direction of the U–U bonds is the “soft” crystallographic direction.
► Highest coefficient of linear thermal expansion is in the direction of the U–U bonds.
► The closer the U atoms are together the better they can be compressed together.