Structure of the mixed-valence lithium cuprate Li3Cu2O4 by powder neutron diffraction

Abstract

The structure of Li₃Cu₂O₄ has been refined from time-of-flight powder neutron diffraction data in order to define accurately the copper–oxygen coordination geometry and lithium-ion positions. The structure consists of slightly distorted, square-planar CuO₄ units sharing opposite edges to form infinite chains running parallel to the b axis. Lithium ions were found to occupy two types of site in the structure: (1) a distorted tetrahedral site found previously, and (2) two disordered sites displaced from a mean octahedral position. The disorder in the lithium ions is similar to that observed in ferroelectric materials such as LiTaO₃ below their Curie temperature. Bond lengths around copper support its non-integral valence, and bond-valence calculations are performed for all cation sites.