Substitutional disorder in the system Mg1 − x Cu2 + x O3: Cu2+ in a compressed octahedral environment

Abstract

Abstract In the system Mg1 − x Cu2 + x O3 the phase with x = 0, i.e. the compound MgCu2O3, does not exist. Neutron powder measurements and single crystal X-ray studies clearly show that the Mg lattice site is partially occupied by Cu2+ ions with typical values of x = 0.1. This substitutional disorder, best denoted by the formula (Mg1 − xCux)Cu2O3, is surprising, since the coordination polyhedron of the Mg site is a compressed oxygen octahedron, while the Jahn-Teller ion Cu2+ usually prefers a tetragonally elongated oxygen octahedron, as it exists on the regular Cu site of the lattice. The local environment of the Cu2+ ions on the Mg site was also checked by electron paramagnetic resonance (EPR) measurements.