Phase transition of LixNa1-xNbO3 studied by Raman scattering method

In this study, we use X-ray diffraction and Raman scattering techniques to study the structure and phase transition of lithium sodium niobate crystal. Raman scattering experiments on these ceramics have been performed in the temperature range from 300 to 77 K. All the spectral lines in the Raman spe ctra can be assigned as the transitional modes of cations Li+ and Na+ and t he internal modes of NbO6 octahedron. From the evolution of the spectral li ne in the Raman spectra at various temperatures, we conclude that phase tra nsition of all three crystals of x = 0.1, 0.12, 0.15 occurs over a temperat ure range from 200 to 180 K on the cooling process and at 280 K in the heat ing process. The phase transition of other compositions is also similar to the pure sodium niobate, but the transition temperatures are different. The lattice structure at room temperature was also studied by X-ray diffrac tion. The study shows that the crystal demonstrates a single phase of ortho rhombic structure for x less than or equal to 0.15, two phases above x = 0. 2, and then changes to LiNbO3 structure until x = 0.9. These results agree well with the results from x-dependent Raman scattering experiments. From t emperature-dependent Raman scattering study, we have shown that the Raman s pectra of LixNa1-xNbO3 exhibit a phase transition below room temperature th at is similar to that observed in NaNbO3. The transitional motion of the Na + cation may be involved in the structural phase transition of lithium sodi um niobate. (C) 1999 Elsevier Science Ltd. All rights reserved.