Studies of ferroelectric and magnetic phase transitions in multiferroic PbFe_0.5Ta_0.5O₃–PbTiO₃ solid solution ceramics

Dielectric, X-ray, Mossbauer and magnetization studies of (1 − x)PbFe_0.5Ta_0.5O₃–(x)PbTiO₃ ceramics with 0 ≤ x ≤ 0.3 have been carried out to determine the compositional evolution of ferroelectric and magnetic phase transition temperatures. Addition of PbTiO₃ to PbFe_0.5Ta_0.5O₃ increases the temperature T _m of the dielectric permittivity maximum, decreases both the diffusion of this maximum and its frequency dependence. However, the Curie–Weiss temperature exceeds T _m for all the compositions studied, indicating that the phase transition still remains diffused. Dilution of the (Fe, Ta)-sublattice by Ti lowers the Neel temperature T _N but above a certain compositional threshold (x ≈ 0.1) fast lowering of T _N stops and a new magnetic state stable in a rather wide compositional range appears. Large difference between the zero-field-cooled (ZFC) and FC magnetization–temperature curves as well as between the temperatures of magnetic phase transition determined from Mossbauer and magnetization studies for compositions with x > 0.1 implies that this state is a spin-glass phase.