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Elastic Anomalies Associated with the Antiferroelectric Phase Transitions of PbHfO3 Single Crystals
고재현,Krystian Roleder,Andrzej Majchrowski,Annette Bussmann-Holder 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.8
The temperature dependence of the elastic properties of antiferroelectric PbHfO3 was investigatedby using Brillouin scattering. The two structural phase transitions of antiferroelectricantiferroelectric-paraelectric phases were clearly identified from the discontinuous changes in theacoustic mode frequencies and the hypersonic damping. The substantial softening of the modefrequency, along with the remarkable increase in the acoustic damping observed in the paraelectricphase, indicated the formation of precursor noncentrosymmetric (polar) clusters and their couplingto the acoustic waves. This was corroborated by the observation of quasi-elastic central peaks,the intensity of which grew upon cooling toward the Curie point. The obtained relaxation timeexhibited a slowing-down behavior, suggesting that the dynamics of the precursor clusters becamemore sluggish on approaching the phase transition temperature.
이정우,고재현,Krystian Roleder,D. Rytz 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.74 No.11
Elastic anisotropy and slowness curves of barium titanate (BaTiO$_3$) single crystal in the paraelectric phase were investigated by using Brillouin spectroscopy. The directional dependence of sound velocities of the longitudinal and the transverse acoustic waves in the (001) plane showed a four-fold symmetry typical in the cubic phase. Especially, one of the two transverse modes exhibited a substantial softening along the $<$110$>$ directions. The sound velocity of this mode decreased significantly as temperature decreased toward the transition temperature, which corresponded to the elastic stiffness coefficient (C$_{11}$ $-$ C$_{12}$)/2. This result suggests the tetragonal instability caused by the precursor polar clusters in the paraelectric phase of BaTiO$_3$.
이정우,고재현,Krystian Roleder,D. Rytz 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.75 No.5
The effects of rhodium (Rh) doping on the elastic properties and phase transition behaviors of reduced BaTiO$_3$ single crystals were investigated in the paraelectric phase by using Brillouin spectroscopy. The Rh doping induced changes in the elastic stiffness coefficients and the elastic anisotropy parameter. The degree of softening of ($C_{11} - C_{12}$)/2 became more substantial with Rh doping, indicating that the polarization fluctuations were enhanced by heterovalent Rh$^{3+}$ doping. This was supported by the much larger temperature range over which the nonzero birefringence was observed. Free charge carriers introduced by Rh doping and oxygen vacancies in the reduced BaTiO$_3$ and their interactions with the lattice seem to be the origin of these anomalous changes in the elastic properties.