  Lead vanadate PbVO3 is a polar crystal with a P4mm space group at ambient
conditions. It is isostructural with the model soft-mode driven ferroelectric
PbTiO3, but differs from it by the so-called 'supertetragonal' elongation of
its unit cell. In this paper, we report a combined study of the lattice
dynamics of PbVO3 by Raman spectroscopy at room temperature and first-principle
calculations. All zone-center transverse optical (TO) phonon modes are
identified by polarized, angle-dependent Raman spectroscopy and assigned as
follows: E modes at 136, 269, 374 and 508 cm-1, A1 modes at 188, 429 and 874
cm-1 and B1 mode at 319 cm-1. The calculations confirm the experimental
symmetry assignment and allow to obtain the longitudinal (LO) phonons
wavenumbers. Besides, we analyze the mode eigenvectors in detail, in order to
identify the atomic displacements associated with each mode and compare them
with PbTiO3. In spite of their differences in chemistry and strain, the phonon
eigenvectors are found to be remarkably comparable in both compounds. We
discuss the position of the ferroelectric soft mode in PbVO3 as compared to
PbTiO3. A sizeable splitting of the B1+E modes appears as a characteristic
feature of supertetragonal phases. The peculiarity of the vanadyl V-O bond
frequency in PbVO3 is also addressed.
