  Raman Spectroscopic measurements are carried out to investigate the
structural phase transitions as a function of composition in modified sodium
niobate [(1-x) NaNbO3-xBaTiO3:NNBTx] for x=0.0 to 0.15 at room temperature. The
characteristic antiferroelectric modes at around 93.4 and 123.6cm-1alongwith a
mode at 155.5 cm-1were found to disappear across the structural phase
transition from antiferroelectric orthorhombic phase (Pbcm) to ferroelectric
orthorhombic phase (Pmc21) phase for x>0.02. The redistribution of intensities
and positions of the Raman lines in bending (150-350 cm-1) and stretching modes
(>550cm-1) on increasing the concentration x>0.05 also confirms the occurrence
of another phase transition from ferroelectric orthorhombic phase (Pmc21) 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.
