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A new indium terbium germanate InTbGe2O7, which is a member of the thortveitite family, was prepared as a polycrystalline powder material by high-temperature solid-state reaction. This new compound crystallizes in the monoclinic system, space group C2/c (No. 15), with unit cell parameters a = 6.8818(2)Angstrom, b = 8.8774(3)Angstrom, c = 9.7892(4)Angstrom, beta = 101.401 (1)degrees V = 586.25(4)Angstrom(3) and Z = 4. Its structure was characterized by Rietveld refinement of powder laboratory X-ray diffraction data. It consists of octahedral sheets that are held together by sheets of isolated Ge2O7 diorthogroups composed of two tetrahedra sharing a common vertex. It contains only one octahedral site occupied by In3+ and Tb+3 cations. The characteristic mirror plane in the thortveitite (SC2Si2O7) space group (C2/m, No. 12) is not present in this new compound. Besides, in InTbGe2O7, the Ge-O-Ge angle bridging two diorthogroups is 156.8(2)degrees as compared to the one in thortveitite, which is 180degrees. On the other hand, luminescent properties were observed when it is excited with 376.5 nm wavelength. The luminescence spectrum shows typical transitions from the D-5(4) multiplet belonging to the trivalent terbium ion. (C) 2003 Elsevier Science (USA). All rights reserved. |
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