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 Tc = 18 K the TO1 line softens towards a Raman shift of 7 cm−1. It splits into three components below Tc, which reach 5, 10 and 15 cm−1, respectively, as T → 0. Orthorhombic strain at T < Tc causes morphic intraplanar LB and splitting of the Eg mode originating from the cubic-totetragonal structural transition at T0 = 125 K. Breaking of inversion symmetry at T < Tc initiates second-harmonic generation, first-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.