TEMPERATURE-DEPENDENT RAMAN-SCATTERING STUDIES OF LI0.02NA0.98NBO3

Raman studies of Li0.02Na0.98NbO3 ceramics were observed in the temper ature range between 10 and 300 K. The spectral pattern evolves gradual ly at a transition temperature (130-170 K) in the cooling process and then changes suddenly near 280 K on heating. The observed thermal hyst eresis of 110 K and also the transition temperatures agree well with e vidence coming from the differential scanning calorimetric, the dielec tric constant, and the thermal expansion measurements. The observed sp ectra are discussed following the separation of modes into internal st retching modes of the NbO6 octehedron and cation translation modes. Th e 62- and 74-cm(-1) peaks are proposed due to the translational modes of Na+ cation.