Lattice dynamics and antiferroelectricity in PbZrO$_3$ tested by X-ray   and Brillouin light scattering
  We report the results of comprehensive study of the critical dynamics of the prototype perovskite antiferroelectric PbZrO$_3$. The combination of inelastic X-ray and diffuse X-ray scattering techniques and Brillouin light scattering was used. It is found that the dispersion of the TA phonons is strongly anisotropic. The dispersion curve of the in-plane polarized TA phonons propagating in [1 1 0] direction demonstrates pronounced softening. Slowing down of the excitations at R-point is found, it is manifested in growing of the central peak. This slowing down is too weak to be considered as a primary origin of the corresponding order parameter. Obtained results are treated in terms of TA--TO flexoelectric mode coupling. It is demonstrated that the structural phase transformation in PbZrO$_3$ can be considered as the result of the only intrinsic instability associated with the ferroelectric soft mode. 
R. G. Burkovsky, A. K. Tagantsev, K. Vaideeswaran, N. Setter, S. B.   Vakhrushev, A. V. Filimonov, A. Shaganov, D. Androniko...
cond-mat.mtrl-sci