The ternary phases Cu_1.5-xLi_1+xSb and Cu_4+xLi_1-xSb₂, and their structural relations

In the course of investigations on the phase relations in the Cu-Li-Sb system, two yet unknown ternary phases, namely Cu1.5−xLi1+x Sb and Cu4+xLi1−x Sb2 were synthesized and characterized by powder and single crystal X-ray diffraction experiments. Both title compounds show hexagonal symmetry (a=4.3593(10)/4.2512(9), c=14.445(5)/22.336(7) Å, space groups P63mc and P6̅m2). Strong structural relations are evident among each other and to the compound Cu2−xLi1−x Sb (a=4.3415(8), c=7.448(2) Å, space group P63/mmc). The symmetry change of the different structures goes along with a multiplication of c whereas the lattice parameter a is roughly maintained. The Sb atoms are more or less ordered. Cu and Li atoms are extensively disordered, vacancies are common. The substructure formed by the Sb atoms is densely packed, the stacking sequence of the compounds Cu1.5−xLi1+x Sb, Cu4+xLi1−x Sb2 and Cu2−xLi1−x Sb is ABAC, ABCACB, and AB, respectively.