Quantum effects in incipient and low-temperature ferroelectrics (a review)

The paper discusses the theory of quantum effects in incipient and low-temperature ferroelectrics and its application to the description of some phenomena observed in SrTiO3, KTaO3, and solid solutions based on these compounds. Two approaches are considered, namely, the Barrett theory in the framework of the single-ion (one-sublattice) Devonshire-Slater model and the Rechester and Khmel’nitski 0. 5em{}l -Shneerson theories developed in terms of a soft ferroelectric (polar TO) mode dressed by its anharmonic interaction with zero-point and thermal lattice vibrations. Consideration is given to the specific features of an isoelectronic-impurity-induced ferroelectric phase transition in incipient ferroelectrics, the theory of an isotopic-impurity-induced ferroelectric phase transition in incipient ferroelectrics, the theory of the isotopic Curie-temperature shift in low-temperature ferroelectrics, and the electric-field effect on the dielectric properties of incipient and low-temperature ferroelectrics.