Antiferroelectrics are essential ingredients for the widely applied piezoelectric and ferroelectric materials: the most common ferroelectric, lead zirconate titanate is an alloy of the ferroelectric lead titanate and the antiferroelectric lead zirconate. Antiferroelectrics themselves are useful in large digital displacement transducers and energy-storage capacitors. Despite their technological importance, the reason why materials become antiferroelectric has remained allusive since their first discovery. Here we report the results of a study on the lattice dynamics of the antiferroelectric lead zirconate using inelastic and diffuse X-ray scattering techniques and the Brillouin light scattering. The analysis of the results reveals that the antiferroelectric state is a 'missed' incommensurate phase, and that the paraelectric to antiferroelectric phase transition is driven by the softening of a single lattice mode via flexoelectric coupling. These findings resolve the mystery of the origin of antiferroelectricity in lead zirconate and suggest an approach to the treatment of complex phase transitions in ferroics.
Controversy in the description/identification of so-called intermediate phase (s) in PbHfO 3 , stable in the range $420-480 K, has existed for a few decades. A synchrotron diffraction experiment on a partially detwinned crystal allowed the structure to be solved in the superspace group Imma(00)s00 (No. 74.2). In contrast to some previously published reports, in the pure compound only one distinct phase was observed between Pbam PbZrO 3 -like antiferroelectric and Pm3m paraelectric phases. The modulation vector depends only slightly on temperature. The major structure modulation is associated with the displacement of lead ions, which is accompanied by a smaller amplitude modulation for the surrounding O atoms and tilting of HfO 6 octahedra. Tilting of the octahedra results in a doubling of the unit cell compared with the parent structure.
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.
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