Phase transformations in multiferroic Bi1−xLaxFe1−yTiyO3 ceramics probed by temperature dependent Raman scattering

Abstract

Optical phonons and phase transitions of Bi1−xLaxFe1−yTiyO3 (BLFTO, 0.02 ≤ x ≤ 0.12, 0.01 ≤ y ≤ 0.08) ceramics have been investigated by Raman scattering in the temperature range from 80 to 680 K. Four phase transitions around 140, 205, 570, and 640 K can be observed. The Raman modes are sensitive to the spin reorientation around 140 and 205 K, owing to the strong magnon-phonon coupling. The transformation around 570 K is a structural transition from rhombohedral to orthorhombic phase due to an external pressure induced by the chemical substitution. The anomalies of the phonon frequencies near Néel temperature TN have been discussed in the light of the multiferroicity. Moreover, it was found that the structural transition temperature and TN of BLFTO ceramics decrease towards room temperature with increasing doping composition as a result of size mismatch between substitution and host cations.