"Local phase transitions" and related relaxation processes in incipient ferroelectrics with a perovskite-like structure

The review of recent experimental and theoretical results presented here shows the important role of the local phase transitions (LPT) phenomena in low temperature dynamics of weakly doped KTaO 3 and SrTiO 3 incipient ferroelectrics. An unusual behaviour of zero-phonon R-luminescence line of Cr 3+ centers in KTaO 3 and SrTiO 3 and radio-frequency dielectric permittivity and losses of weakly doped KTaO 3 are discussed in detail. The important role of LPT for local electronic impurity centers as well as for impurity clusters (pairs) of interacting relaxators is demonstrated. A new mechanism of off-center effect for impurity centers at the absence of local charge compensation is proposed.