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Pressure-induced phase transitions in ferroelectric Bi2MoO6—a Raman scattering study

A high pressure Raman scattering study of Bi2MoO6, a member of the bismuth layered Aurivillius family of ferroelectrics, is presented. This study showed the onset of two reversible second-order phase transitions near 2.8 and 7.0 GPa. The pressure dependence of the Raman bands provides strong evidence that the structural changes in Bi2MoO6 are mainly related to the rigid rotations of MoO6 octahedra. Symmetry increases upon application of pressure and the first phase transition involves, most probably, the loss of the MoO6 tilt mode. This structural change may be the same as that observed at ambient pressure at elevated temperature (from P 21ab to a polar orthorhombic structure of unknown symmetry). The second phase transition is associated with some subtle structural changes and the structure above 7.0 GPa is most probably still orthorhombic.