Anomalous changes in the acoustic properties and central peak behaviors of PbxBa1−xNb2O6 single crystals with x = 0.5 studied by Brillouin spectroscopy

The acoustic properties of tetragonal PbxBa1−xNb2O6 (PBN-x) single crystals with x = 0.5 were studied by Brillouin spectroscopy over a wide temperature range from room temperature to 600 °C. Anomalous changes in the Brillouin frequency shift and the half width of acoustic waves were observed at ∼350...

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Bibliographic Details
Published in:Journal of applied physics 2020-11, Vol.128 (18)
Main Authors: Naqvi, Furqan Ul Hassan, Ko, Jae-Hyeon, Lim, Ki-Soo
Format: Article
Language:English
Subjects:
Acoustic properties
Acoustic velocity
Acoustic waves
Acoustics
Anisotropy
Anomalies
Applied physics
Damping
Elastic properties
Ferroelectric materials
Ferroelectricity
Frequency shift
Order parameters
Phase transitions
Phonons
Relaxation time
Room temperature
Single crystals
Softening
Spectroscopic analysis
Spectrum analysis
Transition temperature
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Summary:The acoustic properties of tetragonal PbxBa1−xNb2O6 (PBN-x) single crystals with x = 0.5 were studied by Brillouin spectroscopy over a wide temperature range from room temperature to 600 °C. Anomalous changes in the Brillouin frequency shift and the half width of acoustic waves were observed at ∼350 °C that corresponds to the ferroelectric–paraelectric phase transition temperature of PBN-0.50. The longitudinal sound velocity and its associated elastic constant (C33) showed substantial softening in the paraelectric phase when the phonon propagated along the polar c axis, while their degree of softening for the phonon along the a axis was small, revealing clear acoustic anisotropy. It was associated with the strong polarization dependence of the quasi-elastic central peak. The relaxation time derived from the central peak seemed to follow the critical slowing-down behavior indicating order–disorder nature of the phase transition. Among C44 and C66, the former displayed substantial softening in the ferroelectric phase resembling the order parameter behavior. The longitudinal sound velocity and the related acoustic damping showed significant anomalies in the ferroelectric phase of unpoled PBN-0.5, which disappeared completely under poled condition. The possible origin for these unexpected acoustic anomalies was suggested.
ISSN:0021-8979
1089-7550
DOI:10.1063/5.0032273