Phase transitions in SrTiO3 quantum paraelectric with impurities

Phase diagrams of SrTiO3-based solid solutions with PbTiO3, BaTiO3, and CaTiO3 have been analyzed using our own experimental data and some data from the literature on dielectric, ultrasonic, and optical properties. At small concentration x of the second end-member of solid solutions, ferroelectric phase transition temperature varies as T-c= A(x-x(c))(1/2) where the critical concentration x(c) is almost the same for all the impurities: x(c) = 0.002. At high x values, the T-c(x) dependences are linear. For the case of PbTiO3 and BaTiO3, the structural and ferroelectric phase transition lines in the (T - x) plane converge at x near 0.04.