In1.08Gd0.92Ge2O7: a new member of the thortveitite family

Indium gadolinium digermanium heptaoxide, In_1.08Gd_0.92Ge₂­O₇, with a thortveitite‐type structure, has been prepared as a polycrystalline powder material by a high‐temperature solid‐state reaction. As in the mineral thortveitite, the crystal structure belongs to the monoclinic system, with space group C2/m (No. 12). The precise structural parameters were obtained by applying the Rietveld method of refinement to the X‐ray powder diffraction data. This layered structure presents, on one side, a honeycomb‐like arrangement of the unique octahedral site, which is occupied randomly by In and Gd atoms, and, on the other side, sheets of isolated Ge₂O₇ diortho‐groups made up of double tetrahedra sharing a common vertex and displaying C_2h point symmetry. This compound showed a remarkable photoluminescence effect when it was irradiated with the X‐ray beam during the X‐ray diffraction measurements, and with the α beam during the Rutherford back‐scattering spectrometry experiments employed to analyze the chemical stoichiometry.