Soft-mode spectroscopy and pyroelectricity in KTaO3:Na

Raman spectra are reported for samples of KTaO3 as a function of concentration, scattering geometry, and field treatments. A first-order Raman effect is observed in the polar phase indicating that the axial distortions of the lattice in the polar phase are correlated up to several 1000 A. Pyroelectric and susceptibility data indicate that the polar directions of these distortions are less correlated than axial distortions. The low-temperature phase consists of dipoles in predominantly parallel-antiparallel alignment within large regions of constant axial anisotropy. Attempts are made to estimate the extent of polar order and to relate it to the frustrated dipolar random forces. © 1987 The American Physical Society.