The ternary phases CuLi_2−xSb, Cu_2−xLi_1+xSb, and Cu_2−xLi_1−xSb and their structural relations to binary alloys in the systems Cu−Sb and Li−Sb

In the course of studies on the phase relations in the system Cu-Li-Sb at 400 °C the ternary compounds CuLi _2-x Sb, Cu _2-x Li _1+x Sb and Cu _2-x Li _1-x Sb were synthesized by melting processes followed by long-time annealing procedures. They were chemically as well as structurally characterized. Powder and single-crystal X-ray diffraction investigations proved that CuLi _2-x Sb crystallizes cubic (space group F4?3m, a=6.248(2) Å) and Cu _2-x Li _1-x Sb hexagonal (space group P6 ₃/mmc, a=4.3415(8) Å, c=7.448(2) Å). For Cu _2-x Li _1+x Sb the average structure is cubic (space group Fm3?m, a=6.169(2) Å). However, it was not possible to unravel split reflections seen in the single-crystal diffraction images. Powder X-ray diffraction patterns gave a hint for tetragonal symmetry (a=4.3832(1) Å, c=6.0512(2) Å). It is assumed, that Cu _2-x Li _1+x Sb is formed from Cu-rich CuLi _2-x Sb in a second order transition reaction during cooling; single domains could not be separated. The three title compounds show close structural relations among each other as well as to the binary compounds Li ₃Sb (P6 ₃/mmc and Fm3?m modifications), β-Cu ₃Sb (Fm3?m), η-Cu ₂Sb (P4/nmm) and δ-Cu ₄Sb (P6 ₃/mmc). In all cases, the Sb atoms are in a fully ordered ccp or hcp arrangement. In between are the Cu and Li atoms. They exhibit an extensive disorder due to both, mixed and partial occupations making the alloy system Cu-Li-Sb a candidate for electrode materials to be used in Li-ion batteries.