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

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Abstract
CdGa2O4, CuGa2O4 and four ternary spinels CdxCu1–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 CdxCu1–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.
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