Quantum paraelectricity in the mean-field approximation

Recently discovered [W. Kleemann et al., Phys, Rev.: B 58, 8985 (1998)] sca ling properties of the electric susceptibility of quantum paraelectric soli d solutions SrTiO3:Ca are shown to emerge from a Landau-type free-energy fu nction involving the quantum temperature T-Q = T-s coth(T-s/T) of Salje et al. [Z. Phys. B 82, 399 (1991)]. It is derived from both the Salje-Wruck-Th omas model and the transverse Ising model and applies also to cases where n o phase transition is encountered. [S0163-1829(99)02045-7].