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Open AccessArticle

Acoustic Anomalies and Phase Transition Behaviors of Lead-Free Piezoelectric (Na1/2Bi1/2)TiO3-xBaTiO3 Single Crystals as Revealed by Brillouin Light Scattering

1
Department of Physics, Hallym University, Chuncheon, Gangwon-do 24252, Korea
2
Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 201800, China
*
Author to whom correspondence should be addressed.
Materials 2018, 11(6), 1000; https://doi.org/10.3390/ma11061000
Received: 23 May 2018 / Revised: 9 June 2018 / Accepted: 10 June 2018 / Published: 12 June 2018
(This article belongs to the Special Issue Piezoelectric Materials and Devices)
The elastic properties of unpoled and prepoled (Na1/2Bi1/2)TiO3-xBaTiO3 (NBT-xBT) single crystals near the morphotropic phase boundary were investigated as a function of temperature using Brillouin light scattering. The acoustic mode frequency and the related acoustic damping of unpoled NBT-xBT showed very broad minimum and maximum, respectively, consistent with typical relaxor behaviors. The frequency softening of the longitudinal acoustic mode together with the increase in acoustic damping was largest along the <100> direction, indicating that polarization fluctuations were most substantial along this crystallographic direction. The difference in acoustic behaviors between the unpoled NBT-xBTs with x = 0.05 and 0.08 were negligible, which means that the NBT-xBT system exhibits typical relaxor properties over a certain composition range of at least 5~8%. The obtained relaxation time of polar nanoregions in the paraelectric phase showed a gradual slowing-down character without any critical divergent behavior. The prepoling of NBT-xBT along the <100> direction induced drastic changes in both mode frequency and damping at ~110 °C when the poling field was larger than 1.4 kV/mm, corresponding to the depoling process from macroscopic/mesoscopic ferroelectric order to ergodic relaxor state upon heating. Phase coexistence of ferroelectric and relaxor states was observed at the intermediate poling field of 1.4 kV/mm. View Full-Text
Keywords: NBT-BT; lead-free; relaxor; polar nanoregion; Brillouin scattering NBT-BT; lead-free; relaxor; polar nanoregion; Brillouin scattering
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Lee, B.W.; Oh, S.H.; Ko, J.-H.; Li, X.; Luo, H. Acoustic Anomalies and Phase Transition Behaviors of Lead-Free Piezoelectric (Na1/2Bi1/2)TiO3-xBaTiO3 Single Crystals as Revealed by Brillouin Light Scattering. Materials 2018, 11, 1000.

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