Structural characterization of cadmium–copper gallium oxide (CdxCu1–xGa2O4) spinels

Abstract

CdGa₂O₄, CuGa₂O₄ and four ternary spinels Cd_xCu_1–xGa₂O₄ have been prepared by solid-state reaction of mixtures of CdO, CuO and Ga₂O₃ at 1223 K. X-ray powder diffractometry has been used to determine the unit-cell parameter, a₀, the oxygen parameter, u, and the respective distributions of Cd²⁺, Cu²⁺ and Ga³⁺ in tetrahedral and octahedral coordination, by applying a computational method to compare observed and calculated diffraction intensities. The capability of the method has been tested for CuGa₂O₄, where the Cu²⁺(3d⁹) and Ga³⁺(3d¹⁰) ions have similar scattering powers, by comparing the results with data from neutron diffraction.

CdGa₂O₄ and CuGa₂O₄ are 15 and 84% inverse, respectively. Interdependence of a₀, u and the cation distribution is closely analysed for Cd_xCu_1–xGa₂O₄, where the behaviour of the ternary system gives new insight into the oxide crystal chemistry. The steric effects on lattice distortion are discussed alongside the covalent contribution in the metal–oxygen bonds, which is manifested in the strong tetrahedral preferences of Cd²⁺ and Ga³⁺ ions.