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

Abstract

We report the results of comprehensive study of the critical dynamics of the prototype perovskite antiferroelectric PbZrO3. 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 PbZrO3 can be considered as the result of the only intrinsic instability associated with the ferroelectric soft mode.

Phonon dispersion calculations using the Vaks model in antiferroelectric lead zirconate

“…In this case, anisotropic mode coupling parameter V a was put as zero. Parameters S a , S t , V t were fitted to produce the best agreement with the whole set of the data 7,8 (TA inplane and TA out-of-plane phonons). The next parameter values have been obtained: 2 .…”

“…7,8,12 The incommensurate phase is expected when the factor becomes larger than one. It has been reported 7,8 that for PZ this factor is 0.9.…”

“…It has been proposed 7,8 that in PZ this ferroelectric instability, due to the flexoelectric mode coupling, pushes down the transverse acoustic (TA) phonon branch. As a result, PZ exhibits anomalously low and almost flat TA phonon branch propagating along [110] direction with polarization vector e ¼ ð1 À 10Þ (so-called \in-plane" polarization).…”

“…However, the PZ undergoes first-order phase transition at temperature about 500 K with commensurate wave vector q ¼ ; 0Þ because of umklapp process. 7,8 The factor which determines the possibility of incommensurate phase transition has been proposed. 7,8,12 The incommensurate phase is expected when the factor becomes larger than one.…”

“…7,8 The factor which determines the possibility of incommensurate phase transition has been proposed. 7,8,12 The incommensurate phase is expected when the factor becomes larger than one. It has been reported 7,8 that for PZ this factor is 0.9.…”