Mode Coupling at around M-Point in PZT.

Sergey Vakhrushev,Alexei Bosak,Konstantin Petroukhno,Igor Leontyev,Alexey Filimonov,Andrey Rudskoy,Stanislav Udovenko

doi:10.3390/ma15010079

Abstract

The question of the microscopic origin of the M-superstructure and additional satellite peaks in the Zr-rich lead zirconate-titanate is discussed for nearly 50 years. Clear contradiction between the selection rules of the critical scattering and the superstructure was found preventing unambiguous attributing of the observed superstructure either to the rotation of the oxygen octahedra or to the antiparallel displacements of the lead cations. Detailed analysis of the satellite pattern explained it as the result of the incommensurate phase transition rather than antiphase domains. Critical dynamics is the key point for the formulated problems. Recently, the oxygen tilt soft mode in the PbZrTiO (PZT2.4) was found. But this does not resolve the extinction rules contradiction. The results of the inelastic X-ray scattering study of the phonon spectra of PZT2.4 around M-point are reported. Strong coupling between the lead and oxygen modes resulting in mode anticrossing and creation of the wide flat part in the lowest phonon dispersion curves is identified. This flat part corresponds to the mixture of the displacements of the lead and oxygen ions and can be an explanation of the extinction rules contradiction. Moreover, a flat dispersion surface is a typical prerequisite for the incommensurate phase transition.

Highlights

In the last few decades, the interest in antiferroelectric (AFE) materials [1] has grown sharply
Lead zirconate is a classic perovskite-like antiferroelectric, while lead titanate is perovskite-like ferroelectric
The phase diagram of the PZT at x ≤ 0.06 was reported in the papers [6,7] and it was shown that these compounds are antiferroelectrics (AFE) at room temperature

Summary

Introduction

In the last few decades, the interest in antiferroelectric (AFE) materials [1] has grown sharply. The phase diagram of the PZT at x ≤ 0.06 was reported in the papers [6,7] and it was shown that these compounds are antiferroelectrics (AFE) at room temperature. All those compounds have a simple cubic (C) structure in the paraelectric phase. In most of these materials, the phase transition to the AFE phase occurs through an intermediate ferroelectric phase (IFE) [8,9,10]. The structure of the AFE phase can be considered as well established, while the structure of the intermediate FE phase remains questionable, despite of the may papers on this subject

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Conclusion