Raman-scattering study of stress-induced ferroelectricity in KTaO3

The stress-induced ferroelectricity in KTa${\mathrm{O}}_3$ is investigated by means of Raman scattering at 2 K. In the (010)-stress-induced ferroelectric phase, the transverse soft $A_1$, $B_1$, and $B_2$ modes have been observed as a first-order Raman scattering and are found to increase their frequencies with the stress in accordance with the Lyddane-Sachs-Teller relation. The $A_1$ Raman line is found to broaden as the stress approaches the transition stress. From the stress dependence of the soft-mode frequencies, the transition stress is estimated as 5.25 kbar in agreement with a previous dielectric observation. Values of the nonlinear dielectric susceptibilities are obtained from a comparison of a phenomenological theory to the experimental results. Furthermore, the effective charge of the soft mode is evaluated and the value is compared with previous data. From the first- and second-order Raman spectra up to 1200 ${\mathrm{cm}}^{-1\mathrm{}}$, zone-center phonons and pairs of phonons at critical points in the Brillouin zone are identified, and their stress dependence, especially for the 2TA overtone, is investigated.