Structural ordering principles in quasi one-dimensional Wigner crystals of the series Na1+x CuO2 (0 ≤ x ≤ 1)

Abstract

Abstract The general building principle of the commensurate subset of mixed valent sodium cuprates Na1+x CuO2 (0 ≤ x ≤ 1) has been revealed. Starting from parent ­NaCuO2, spin doping of the chain of edge sharing CuO4 plaquettes requires to incorporate further sodium ions for charge compensation. The accessible space needed for this purpose is generated by elongating the NaO6 octahedra present in NaCuO2. In this way, from one octahedron two square pyramidal and two tetrahedral sites result, out of which at best one each tetrahedral and square pyramidal site per original octahedron can be occupied, excluding combinations of electrostatically blocked sites. This general building principle has been employed to predict further structure candidates of this series (x = 1/4, 1/3, 2/3, 5/7, 3/4, 1). Density functional calculations (x = 0, 5/7, 3/4, 1) confirm the predicted charge ordering as well as the related structural features. The structure candidates are identified as local minima on the energy landscape.