Doping effect on the phase transition temperature in ferroelectric SrBi_2-xNd_xNb₂O₉ layer-structured ceramics: A micro-Raman scattering study

The temperature dependence of Raman spectra for SrBi_2-xNd _xNb₂O₉ ceramics (x from 0 to 0.2) has been studied in a wide temperature range from 80 to 873 K. It is found that the peak position of the A_1g[Nb] phonon mode at 207 cm^-1, which is directly associated with the distortion of NbO₆ octahedron, decreases with increasing Nd composition, while the A_1g[O] phonon mode at 835 cm^-1 increases. Moreover, both the peak position and intensity of the A_1g[Nb] phonon mode reveal strong anomalies around the ferroelectric to paraelectric phase transition temperature. It indicates that the phase transition temperature decreases from about 710 to 550 K with increasing Nd composition, which is due to the fact that the introduction of Nd ions in the Bi₂O₂ layers reduces the distortion extent of NbO ₆ octahedron.