An X‐Ray Powder Diffraction Study of Phases in the System CuO ‐ NiO ‐ MgO at 1000°C

Abstract

Lattice parameter measurements using x‐ray Guinier techniques found substantial negative deviations from Vegard's law in the system at 600°C. Negative deviations occur at 1000°C for samples containing small concentrations of . Measurements of compositions in the system allow prediction of the lattice constant of having the rocksalt structure. The pressure at which tenorite transforms to its rocksalt modification is estimated to be 335 kbar. An ordered compound, , shows a tetragonal distortion from cubic symmetry. Considerable diffuse scattering was observed in the powder diffraction pattern suggesting a variation in the local cation coordinations. This tetragonal distortion disappears rapidly in the ternary system. The ordered compound is stable well into the ternary system, with strong evidence for Ni²⁺ substitution.