The structure of LiCu2O2 with mixed-valence copper from twin-crystal data

Abstract

The structure of LiCu₂O₂ was solved using two sets of X-ray diffraction twin-crystal data. Extended twinning creates virtual tetragonal symmetry. The compound crystallizes in Pnma (62) with unit-cell parameters $\text{a = 5.72}\text{A}\text{̊}\text{, b = 2.86}\text{A}\text{̊}$ and $\text{c = 12.4}\text{A}\text{̊}$ with a certain homogeneity range. The structure consists of LiCu^IIO₂ layers interleaved by layers of Cu^I connected to oxygen in an almost linear coordination. Lithium and copper(II) have five oxygen neighbours in pyramidal arrangements that run as parallel bands through edge connections. Electron diffraction was used for characterizing the twinning.