Brillouin scattering study of potassium lithium niobate single crystals

Brillouin spectra of two kinds of potassium lithium niobate (KLN) single crystals were investigated, whose compositions were K2.90Li1.91Nb5.06O15 (KLN-1) and K2.60Li1.17Nb5.44O15 (KLN-2). Complete sets of elastic constants for the tetragonal 4mm or 4/mm Ta symmetry, i.e., C-11; C-33, C-44; C-66, C-12 and C-13 were determined from backward scattering and right angle scattering geometries. Only C-33 of KLN-1, which shows a ferroelectric phase transition around 470 degreesC, was much smaller than that of KLN-2 which would show any phase transition. To investigate in more detail, the temperature dependence Of C-33 of KLN-1 was examined from room temperature to 560 degreesC. A significant softening Of C-33 was observed near the phase transition temperature, consistent with the dielectric data.