Local residual stresses in pressure-treated barium titanate powders probed by second harmonic generation

Properties of the barium titanate submicron powder treated by high pressure were studied by nonlinear optic techniques. It is shown that the second harmonic signal at the high temperature phase is reliably observed up to 1000 K. The phase transition is broadened on increasing the pressure value. It is supposed that both the temperature dependence of the second harmonic generation and the broadening of the phase transition are effected by residual mechanical stresses. The annealing decreases residual mechanical stresses and changes the properties of the nonlinear signal towards those of single crystal and submicron powder.