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Coexistence of Ferroelectric Phases and Phonon Dynamics in Relaxor Ferroelectric Na 0.5 Bi 0.5 TiO 3 Based Single Crystals
Author(s) -
Zhu Jiajun,
Zhang Jinzhong,
Jiang Kai,
Zhang Haiwu,
Hu Zhigao,
Luo Haosu,
Chu Junhao
Publication year - 2016
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.14250
Subject(s) - monoclinic crystal system , raman spectroscopy , phonon , ferroelectricity , materials science , dielectric , phase transition , phase (matter) , antiferroelectricity , condensed matter physics , crystallography , crystal structure , optics , chemistry , physics , optoelectronics , organic chemistry
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 Na 0.5 Bi 0.5 TiO 3 , Na 0.5 Bi 0.5 TiO 3 –5%BaTiO 3 , and Na 0.5 Bi 0.5 TiO 3 –8%K 0.5 Bi 0.5 TiO 3 single crystals. It was found that Na 0.5 Bi 0.5 TiO 3 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 + TiO 3 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 Na 0.5 Bi 0.5 TiO 3 , respectively.