Substitutions into the trigonal bipyramidal site of InGaCuO4

Solid solutions of InMCu1−xMgxO4 (M=Ga3+, Al3+) have been synthesized to understand the influence of the trigonal bipyramidal (TBP) crystallographic M3+/Cu2+ site of the YbFe2O4-type structure through powder X-ray and neutron diffraction, dielectric and magnetism measurements. The addition of Mg2+ in the InGaCuO4 lattice results in a decrease of the dielectric constant, but the dielectric loss is not affected until the concentration of Mg2+ is above x=0.50. The shift in the diffraction peaks, and subsequently the change in the lattice parameters, cannot be exclusively explained by the change in ionic radii. These results show the first observation of the reduction in axial bond lengths for TBP Cu2+ in a YbFe2O4-type crystal lattice.