Ferroelectric domain state transition of SrTiO3,:Ca

Second-order Raman scattering at fluctuating ferroelectric microregions is observed as a precursor of the ferroelectric phase transition of Sr].,CaITi03 with x = 0.007 into a low-temperature domain state. On approaching Tc = 18 K the TO, line softens towards a Raman shift of 7 cm. It splits into three components below Tc, which reach S, 10 and IS cm1, respectively, as T -» 0. Orthorhombic strain at T < Tc causes morphic intraplanar LB and splitting of the Efq mode originating from the cubic-to-tetragonal structural transition at T0 = 12S K. Breaking of inversion symmetry at T < Tc initiates second-harmonic generation, first-order Raman scattering of the hard polar TO2 mode at 173 cnr1 and giant photoconductivity. Ferroelectric stripe domains stacked along the c axis of the sample are evidenced by polarizing microscopy and by light diffraction. © 1994, Taylor & Francis Group, LLC. All rights reserved.