NEW, LEAD FREE, FAMILY OF PEROVSKITES WITH A DIFFUSE PHASE TRANSITION: NaNbO3-BASED SOLID SOLUTIONS

(1-x)NaNbO3-(x)ABO3 perovskite solid solutions belonging to group II according to the Krainik classification exhibit a dramatic diffusion of the dielectric permittivity maximum and relaxor-type behavior when the second component concentration exceeds a threshold value x=0. The concentration phase transition to this relaxor-like phase is abrupt (of the first order kind) that is seen from the step in the dependence of the dielectric permittivity(T) maximum temperature, Tm, on x. Some relaxor-like properties appear even at x < x0 in the course of cooling while disappear during the course of heating. Due to this fact and because of coupling of the antiferroelectric (AFE) and ferroelectric (FE) order parameters a giant (up to 100 K) temperature hysteresis of dielectric permittivity(T) arises at AFE-AFE first order phase transition. The Tm values of all the known NaNbO3-ABO3 relaxor-type compositions are well below the RT and the dielectric permittivity maximal values, dielectric permittivity, are much lower than in the case of Pb-containing relaxors. However both Tm and dielectric permittivity values can be increased by Li or K-doping leading to the formation of NaNbO3-ABO3-LiNbO3 (KNbO3) solid solutions. 50 refs.