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 Sr1-xCaxTiO3 with x = 0.007 into a low-temperature domain state. On approaching T-c = 18 K the TO1 line softens towards a Raman shift of 7 cm(-1). It splits into three components below T-c, which reach 5, 10 and 15 cm(-1), respectively, as T -> 0. Orthorhombic strain at T < T-c causes morphic intraplanar LB and splitting of the E-g mode originating from the cubic-to-tetragonal structural transition at T-0 = 125 K. Breaking of inversion symmetry at T < T-c initiates second-harmonic generation, fist-order Raman scattering of the hard polar TO2 mode at 173 cm(-1) and giant photoconductivity. Ferroelectric stripe domains stacked along the c axis of the sample are evidenced by polarizing microscopy and by light diffraction.