Coexistence of Ferroelectric Phases and Phonon Dynamics in Relaxor Ferroelectric Na0.5Bi0.5TiO3 Based Single Crystals. Issue 7 (15th April 2016)

• Record Type: Journal Article
• Authors: Zhu, Jiajun; Zhang, Jinzhong; Jiang, Kai; Zhang, Haiwu; Hu, Zhigao; Luo, Haosu; Chu, Junhao
• Editors: Jones, J.L.
• Is Part Of: Journal of the American Ceramic Society. Volume 99:Issue 7(2016)
• Page Start: 2408
• Page End: 2414
• Publication Date: 2016-04-15
• Subjects: Raman spectroscopy -- relaxor ferroelectrics -- phase transitions; Ceramics -- Periodicals; 620.1405
• DOI: 10.1111/jace.14250
• Languages: English
• ISSNs: 0002-7820

Abstract

Abstract : A combination of polarized Raman technique, infrared reflectance spectra, and first‐principles density‐functional theoretical calculations were used to investigate structure transformation and lattice vibrations of Na0.5 Bi0.5 TiO3, Na0.5 Bi0.5 TiO3 –5%BaTiO3, and Na0.5 Bi0.5 TiO3 –8%K0.5 Bi0.5 TiO3 single crystals. It was found that Na0.5 Bi0.5 TiO3 is of a two‐phase mixture with rhombohedral and monoclinic structures at room temperature. Correspondingly, three Raman‐active phonon modes located at 395, 790, and 868 cm −1, which were previously assumed as A 1 modes of rhombohedral phase have been reassigned as A ′′, A ′, and A ′ modes of monoclinic phase in the present work. In particular, a strong low‐frequency A ′′ mode at 49 cm −1 was found and its temperature dependence was revealed. Two deviations from linearity for the abrupt frequency variation in the A ′′ mode and Ti–O bond have been detected at temperatures of ferroelectric to antiferroelectric phase transition T F–AF and dielectric maximum temperature T max . The appearance of Na–O vibrations at 150 cm −1 was found below T max, indicating the existence of nanosized Na + TiO3 clusters. The observed Raman and infrared active modes belonging to distinct irreducible representations are in good agreement with group‐theory predictions, which suggests 9 A 1 +9 E and 36 A ′′ +24 A ′ modes for the rhombohedral and monoclinic phases of Na0.5 Bi0.5 TiO3, respectively.