Critical Behavior of K1-xLixTaO3 with the Tri-Critical Concentration of Li under an Electric Field

Temperature dependences of the optical second harmonic generation in Li-doped KTaO₃ (KLT) with different Li concentrations x are measured to determine the coefficients in the Landau-Devonshire free energy function. The result specifies the tri-critical Li concentration x_c. Temperature dependences of the dielectric constant of KLT with Li concentrations nearly located at x_c are also measured under dc bias fields and the result suggests that these compounds lie in close vicinity of the line of critical end points. The tertiary phase diagram (T, x, E) of KLT is disclosed from the experiments.