Lattice dynamics and antiferroelectricity inPbZrO3tested by x-ray and Brillouin light scattering

We report the results of a comprehensive study of the critical dynamics of the classical perovskite antiferroelectric ${\mathrm{PbZrO}}_{3}$. 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 transverse acoustic (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-transverse optic (TO) flexoelectric mode coupling. It is demonstrated that the structural phase transformation in ${\mathrm{PbZrO}}_{3}$ can be considered as the result of the only intrinsic instability associated with the ferroelectric soft mode.