Аннотация
High-pressure Raman scattering study of monoclinic beta-BaTeMo2O9 single
crystal was performed. This study showed the onset of two reversible
second-order phase transitions near 3.1 GPa and 7.0 GPa associated with
weak changes of the structure. The pressure dependence of Raman bands
suggests that the phase transitions might involve decrease of the long
Mo-O and Te-O bonds involved in formation of the Mo-O-Mo and Te-O-Mo
bridges, whereas the short Mo-O and Te-O bonds are less affected. These
modifications probably result in tilting on the MoO6 and TeO4 polyhedra
in both phase transitions, although the presence of a strong A(LO) mode
at 13 GPa suggests that the new phases are noncentrosymmetric. Different
behaviour was reported previously in literature for alpha-BaTeMo2O9,
which exhibited a pressure-induced phase transition associated with a
very large change in the coordination sphere of Te4+. Origin of such
different stability of the both BaTeMo2O9 polymorphs under compression
is discussed. (C) 2013 Elsevier B.V. All rights reserved.
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