Evolution of dielectric properties in the (1−x) PbFe_0.5Nb_0.5O₃–xBaFe_0.5Nb_0.5O₃ solid solution system

Temperature dependences of the dielectric permittivity ε of (1−x)PbFe_0.5Nb_0.5O₃-x BaFe_0.5Nb_0.5O₃ solid solution ceramics at 100 Hz–1 MHz have been studied in the 12–500 K temperature range. To lower the conductivity values and exclude the corresponding relaxations, 1 wt% of Li₂CO₃ was added to the starting mixture of oxides. It was found that Li-doping is effective in lowering the conductivity only for compositions with x ≤ 0.5. The permittivity–temperature dependences of the (1−x)PbFe_0.5Nb_0.5O₃–xBaFe_0.5Nb_0.5O₃ compositions were found to change, as x grows, from relatively sharp frequency-independent maxima typical of usual ferroelectrics to the diffused and frequency-dependent maxima typical of relaxors and then to the saturated at low temperatures and frequency-independent ε(T) curves typical of incipient ferroelectrics and at last, to the step-like frequency-dependent ε(T) curves known for the dielectrics with Maxwell–Wagner-type polarization. The ε value of BaFe_0.5Nb_0.5O₃ at 20 K measured at 1 MHz does not exceed 30. The character of the evolution of dielectric properties in the (1−x)PbFe_0.5Nb_0.5O₃–x BaFe_0.5Nb_0.5O₃ system and low ε value of BaFe_0.5Nb_0.5O₃ implies that BaFe_0.5Nb_0.5O₃ is a paraelectric rather than ferroelectric relaxor.