INFRARED SPECTROSCOPY AND THE STRUCTURE OF RARE-EARTH CHROMIUM BORATES RCr3(BO3)4 (R = La-Er)
V. S. Kurazhkovskaya, E. A. Dobretsova, E. Y. Borovikova, V. V. Mal'tsev, N. I. Leonyuk
Keywords: IR spectroscopy, factor group analysis, rare-earth chromium borates
Pages: 721-729
Abstract
Rare-earth chromium borates RCr3(BO3)4, where R = La-Er, obtained as a result of spontaneous solution-melt crystallization and belonging to two polytypic modifications (R32 (D) and С2/с (C) space groups) are studied by infrared spectroscopy with the factor group analysis of vibrations. Borates with R = La-Nd are shown to crystallize in the monoclinic С2/с space group. Borates with R = Sm-Er in the 1:1 ratio of batch and solvent form rhombohedral (R32 space group) and monoclinic (С2/с space group) phases at the 2.3:1 ratio, except EuCr3(BO3)4 and GdCr3(BO3)4 that have the rhombohedral structure under all crystallization conditions. Both rhombohedral and monoclinic polytypes may contain oppositely ordered layers. Y-, Tm-, Yb-, Lu-chromium borates are not formed.
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