Abstract
Lattice dynamics calculations and a high-pressure Raman scattering study
of nanocrystalline Bi2MoO6, a member of the bismuth-layered Aurivillius
family of ferroelectrics, are presented. These studies showed the onset
of two reversible second-order or weakly first-order phase transitions
near 2.5 and 4.5 GPa as well as some subtle structural changes at 8.2
GPa. Symmetry increases upon application of pressure and the first phase
transition involves, most likely, the loss of the MoO6 tilt mode around
a pseudo-tetragonal axis. The second phase transition is associated with
the instability of a low wavenumber mode, which behaves as a soft mode.
This soft mode most likely corresponds to the polar E-u mode of the
tetragonal I4/mmm aristotype and Bi2MoO6 transforms at 4.5 GPa into the
centrosymmetric orthorhombic phase. The sequence of the pressure-induced
phase transitions in nanocrystalline Bi2MoO6 is similar to that observed
for bulk Bi2WO6 but the critical pressures are significantly lower for
the molybdenum compound. Our results also show that the critical
pressure of the first phase transition is slightly lower for the
nanocrystalline Bi2MoO6 (2.5 GPa) than for the microcrystalline (bulk)
Bi2MoO6 (2.8 GPa).
Users
Please
log in to take part in the discussion (add own reviews or comments).