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Mode Coupling at around M-Point in PZT
Sergey Vakhrushev1, Alexey Filimonov2, Konstantin Petroukhno2
1The Ioffe Physical-Technical Institute of the Russian Academy of Sciences, 194021 Saint-Petersburg, Russia.
Materials (Basel, Switzerland)
|January 11, 2022
Summary
The microscopic origin of lead zirconate-titanate
Area of Science:
- Materials Science
- Solid-State Physics
- Crystallography
Background:
- The M-superstructure and satellite peaks in Zr-rich lead zirconate-titanate (PZT) have been debated for 50 years.
- Existing theories face contradictions regarding oxygen octahedra rotations or lead cation displacements.
- Recent findings of an oxygen tilt soft mode in PZT2.4 did not resolve these contradictions.
Purpose of the Study:
- To investigate the microscopic origin of the M-superstructure in PZT.
- To resolve the contradiction between critical scattering selection rules and observed superstructure.
- To understand the role of critical dynamics in PZT phase transitions.
Main Methods:
- Inelastic X-ray scattering (IXS) study of phonon spectra.
- Analysis of PZT2.4 around the M-point.
- Detailed analysis of satellite patterns.
Main Results:
- A strong coupling between lead and oxygen modes was identified.
- Mode anticrossing and a wide, flat phonon dispersion curve were observed.
- This flat dispersion corresponds to mixed lead-oxygen ion displacements, explaining the contradiction.
Conclusions:
- The observed flat phonon dispersion is a prerequisite for incommensurate phase transitions.
- Mixed lead-oxygen ion displacements explain the previously contradictory extinction rules.
- The study provides a new understanding of the M-superstructure's origin in PZT.
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