The crystal structure of FeInGe₂O₇

Abstract

A new iron indium germanate has been prepared as polycrystalline powder material which crystallizes in the monoclinic system (S.G. C2/m, No. 12). The structure was characterized by X-ray powder diffraction and Rietveld refinement of the resulting diffraction pattern. The cell parameters are a = 6.5124(4) Å, b = 8.5914(5) Å, c = 4.8936(3) Å, β = 102.683(2)°, V = 267.12(3) ų and Z = 2. The structure contains R⁺³ cations (R=Fe, In) almost equally distributed in distorted RO₆ octahedral sites. These octahedra are joined by edge sharing forming a hexagonal arrangement on the ab planes. The RO₆ octahedra layers are held together by sheets of isolated Ge₂O₇ diorthogroups constituted by a double tetrahedra sharing a common vertex. This compound has the thortveitite structure and keeps a strong relationship with the FeYGe₂O₇ germanate, which presents two R⁺³ sites with six-coordinated (R=Fe) and seven-coordinated (R=Y) oxygens, corresponding to the different symmetry given by the monoclinic space group P2₁/m (No. 11)