Infrared spectroscopy and the structure of rare earth chromium borates RCr3(BO3)4 (R=La-Er)статья
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Аннотация:Rare-earth chromium borates RCr3(BO3)4, where R = La-Er, obtained as a result of spontaneous solutionmelt crystallization and belonging to two polytypic modifications (R32 (D 3 7 ) and C2/c (C 2h 6 ) 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 C2/c space group. Borates with R = Sm-Er in the 1:1 ratio of batch and solvent form rhombohedral (R32 space group) and monoclinic (C2/c 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.