Short- and long-range polar order contributions to the Ferroelectric phase of Ca2+ doped SrTiO3

Short- and long-range impurity-induced polar ordering in Sr1-xCaxTiO3 (x = 0.014) single crystals was investigated and discussed on the basis of light refraction, morphic birefringence and temperature-dependent dielectric hysteresis loop measurements. Anew method for the calculation of the short-range polar order contribution P-sh in ferroelectric (FE) phases below T-C from light refraction measurements was applied. This method considers optical indicatrix perturbation due to polar ordering taking into account polarization fluctuations. The magnitudes and temperature dependences of P-sh originated by spatial fluctuations and long-range spontaneous polarization P-s were determined. These results allowed us to obtain quantitatively and to compare short (P-sh)-and long (P-s) range polar order contributions to the formation of impurity-induced FE phase in quantum paraelectrics.