Abstract
Raman spectra in a ferroelectrics SrTiO 3 crystal in which 84% 16 O is replaced by the isotope 18 O were studied. Dielectric measurement shows that the sample undergoes a ferroelectric phase transition at 24K. Softening of a peak at 11cm m 1 was found on heating to the transition temperature T c . New peaks also appear at 170cm m 1 and 545cm m 1 below 24K as the result of the condensation of the zone center F 1u modes. Analyzing the spectra in different scattering geometries for the twinned sample, we tentatively assigned the phonon modes assuming that the ferroelectric phase has the symmetry C 2v with the polar axis perpendicular to the tetragonal c axis.
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