The crystal structure of FeInGe2O7

A new iron indium germanate has been prepared as polycrystalline powder mat erial which crystallizes in the monoclinic system (S.G. C2/m. No. 12). The structure was characterized by X-ray powder diffraction and Rietveld refine ment of the resulting diffraction pattern. The cell parameters are a = 6.51 24(4) Angstrom, b = 8.5914(5) Angstrom, c = 4.8936(3) Angstrom, beta = 102. 683(2)degrees, V = 267.12(3) Angstrom (3) and Z = 2. The structure contains R+3 cations (R=Fe. In) almost equally distributed in distorted RO6 octahed ral sites. These octahedra are joined by edge sharing forming a hexagonal a rrangement on the ab planes. The RO6 octahedra layers are held together by sheets of isolated Ge2O7 diorthogroups constituted by a double tetrahedra s haring a common vertex. This compound has the thortveitite structure and ke eps 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 grou p P2(1)/m (No. 11).