SUBSTITUTIONAL DISORDER IN THE SYSTEM MG1-XCU2+XO3 CU2+ IN A COMPRESSED OCTAHEDRAL ENVIRONMENT

In the system Mg1-xCu2+xO3 the phase with x = 0, i.e. the compound MgC u2O3, does not exist. Neutron powder measurements and single crystal X -ray studies clearly show that the Mg lattice site is partially occupi ed by Cu2+ ions with typical values of x = 0.1. This substitutional di sorder, best denoted by the formula (Mg1-xCux)Cu2O3, is surprising, si nce the coordination polyhedron of the Mg site is a compressed oxygen octahedron, while the Jahn-Teller ion Cu2+ usually prefers a tetragona lly elongated oxygen octahedron, as it exists on the regular Cu site o f the lattice. The local environment of the Cu2+ ions on the Mg site w as also checked by electron paramagnetic resonance (EPR) measurements.