Probing of structural phase transitions in barium titanate modified sodium niobate using Raman scattering

Raman spectroscopic measurements are carried out to investigate the structural phase transitions as a function of composition in modified sodium niobate [(1-x) NaNbO3-xBaTiO(3):NNBTx] for x = 0.0 to 0.15 at room temperature. The characteristic antiferroelectric modes at around 93.4 and 123.6 cm(-1), along with a mode at 155.5 cm(-1) were found to disappear across the structural phase transition from antiferroelectric orthorhombic phase (Pbcm) to ferroelectric orthorhombic phase (Pmc2(1)) for x > 0.02. The redistribution of intensities and positions of the Raman lines in bending (150-350 cm(-1)) and stretching modes (>550 cm(-1)) on increasing the concentration x > 0.05, also confirms the occurrence of another phase transition from ferroelectric orthorhombic phase (Pmc2(1)) to another ferroelectric orthorhombic phase (Amm2) phase across x~0.10. The phase transitions as observed from Raman measurements are consistent with previous X-ray diffraction study.