Synthesis, cation distribution and crystal structure of the spinel type solid solution Ga xCoFe 1− xCrO 4 (0⩽ x⩽1)

Abstract

Solid solutions of Ga x CoFe 1− x CrO 4 ( x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0) were obtained by solid-state reactions in air at 1623 K. X-ray and neutron powder diffraction measurements have been performed on the materials in order to characterize them. Rietveld refinement of neutron powder diffraction data showed cubic symmetry corresponding to the space group Fd3m for all samples of the series. The results reveal that Ga has been substituted for Fe selectively. Ga exclusively occupies the octahedral site up to x=0.8, while at x=1.0 a small amount of Ga (5%) enters into the tetrahedral site in the compound. Cr, Fe and Co cations are distributed between the tetrahedral 8a and octahedral 16d sites. Their proportion at each site varies with composition. The fractional coordinates of oxygen are almost the same in all the samples while lattice parameter shows a slight decrease with increasing Ga content. The magnetic structure at room temperature was ferrimagnetic for the composition x=0.0 and 0.2.