Studies of ferroelectric and magnetic phase transitions in multiferroic PbFe0.5Ta0.5O3-PbTiO3 solid solution ceramics

Dielectric, X-ray, Mossbauer and magnetization studies of (1 - x)PbFe0.5Ta0.5O3-(x)PbTiO3 ceramics with 0 a parts per thousand currency sign x a parts per thousand currency sign 0.3 have been carried out to determine the compositional evolution of ferroelectric and magnetic phase transition temperatures. Addition of PbTiO3 to PbFe0.5Ta0.5O3 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 a parts per thousand 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.