Brillouin spectra of K/sub 1-x/Li/sub x/TaO3 under poled and zero-field-cooled conditions

The Brillouin spectra of KTaO3 single crystals containing 5.6 mol % lithium have been investigated as a function of temperature in the temperature range below 77 K. The results obtained for both poled and zero-field-cooled (ZFC) samples are in agreement with the presence of a tetragonal ferroelectric phase below a transition temperature T/sub c/ of approximately 60 K. A 50% step discontinuity was observed in the elastic constant c33 below T/sub c/. The value of the saturated polarization calculated from this change in c33 with the use of electrostrictive data is 0.27 C/m2. The sharp Brillouin components and the anisotropy of the elastic constants in both the ZFC and poled samples imply that the absolute magnitude and axis of the polarization are constant over dimensions on the order of the laser focal spot (i.e., 50--100 μm in diameter). The existence of antiphase domain boundaries between much smaller regions of reversed polarization, however, is suggested by the results of Raman scattering experiments