Ferroelectric microregions and Raman scattering in KTa0(3).

Raman spectra of both nominally pure and deliberately doped KTa0(3) are presented which support the view that symmetry breaking defects induce ferroelectric microregions even far above the bulk T(c) which grow dramatically as temperature is lowered. A characteristic size of these regions is extracted from an analysis of the spectra. The value of R(o)/a varies from nearly 4 at low temperatures to 1.4 at 100 K, the highest temperature where it was determined. For a mixed crystal long range order sets in when these regions become sufficiently large as to occupy the major fraction of the sample's volume. We also find evidence of such regions even in nominally pure KTa0(3), thus implicating very dilute symmetry breaking defects of unknown chemical composition.