Partial Cu occupancy in uranium copper diantimonide, UCu0.60(4))Sb2.

The title compound, UCu(0.60(4))Sb(2), crystallizes in the tetragonal space group P4/nmm. The U atom and one independent Sb atom have 4mm site symmetry, whereas the Cu atom and the other Sb atom have \overline{4}2m site symmetry. Zigzag USb sheets stack perpendicular to the c axis. These sheets are separated by square-planar nets of Sb atoms and Cu atoms. The length of the a axis for UCu(x)Sb(2) is invariant to x, whereas there is a linear relationship between Cu occupancy and the length of the c axis (following Vegard's Law) that holds for x between 0 and 1. This is explained in terms of the crystal structure.