Dielectric and Raman scattering studies of phase transitions in the (100-x)Na0.5Bi0.5TiO3-xSrTiO3 system

Temperature-driven and composition-driven phase transformations in a mixed A-site Pb-free solid solution series of (100-x)Na0.5Bi0.5TiO3-xSrTiO(3) (0 <= x <= 40) were investigated by means of x-ray diffraction, dielectric, and Raman scattering techniques over a temperature range of 20-550 degrees C. The phonon anomalies observed in the room temperature Raman spectra with increasing Sr concentration revealed a morphotropic phase boundary (MPB) at x similar to 20. The distinct and discontinuous changes in dielectric properties at x similar to 20 confirmed the existence of MPB. On heating, the Raman spectral features for different compositions displayed substantial changes at temperatures almost identical to the critical temperatures determined by dielectric measurement, such as ferroelectric-antiferroelectric (T-d), rhombohedral-tetragonal (TR-T), and antiferroelectric-paraelectric (T-m) phase transition temperature. However, the two phonon anomalies observed at higher temperatures (similar to 400 and 500 degrees C for x=10) suggested the coexistence of rhombohedral-tetragonal and tetragonal-cubic phases, respectively. The transition temperatures determined by the Raman and dielectric measurements gradually decreased as Sr concentration increased. The system showed strong relaxor behavior at x >= 20 and the dielectric constant (epsilon) at room temperature was enhanced significantly from similar to 500 (x=0) to similar to 3800 (x=40) at 1 kHz. (C) 2010 American Institute of Physics. [doi:10.1063/1.3490781]