Dielectric, structural, and vibrational properties of (Na0.975Bi0.025) (Nb0.95Ti0.05) O3 at elevated temperature

Abstract

We have studied the dielectric, structural, and vibrational properties of 0.95NaNbO3–0.05(Na0.50Bi0.50)TiO3 (05NBT) solid solution belonging to the NN–NBT family that possess efficient power functionality and large electro-strain. We found that the magnitude of dielectric permittivity increases with temperature and shows diffuse peak anomalies at various temperatures. Detailed analyses of temperature-dependent neutron diffraction patterns revealed that the sample has the ideal cubic perovskite structure above 650 °C. On cooling, it undergoes a series of structural phase transitions from cubic to orthorhombic phases due to condensation of various lattice instabilities. The amplitude of antiferrodistortive distortion mode analysis showed that the value of primary distortive mode decreases on heating and, finally, diminishes at the phase transition temperatures. The displacement patterns corresponding to various lattice instabilities responsible for this structural phase transition are identified. Raman spectra exhibit noticeable changes in the relative intensities between the peaks as well as broadening, merging, and disappearance of certain peaks on heating. The symmetrical and asymmetrical stretching modes (ν1 and ν2) of BO6 octahedra exhibit opposite behavior with temperature while the bending modes merge into a single broad band. This provides clear evidence of local structural changes in the system.