Evolution of dielectric properties in the PbFe.sub.0.5Nb.sub.0.5O.sub.3-xBaFe.sub.0.5Nb.sub.0.5O.sub.3 solid solution system

Temperature dependences of the dielectric permittivity [epsilon] of (1-x)PbFe.sub.0.5Nb.sub.0.5O.sub.3-x BaFe.sub.0.5Nb.sub.0.5O.sub.3 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 Li.sub.2CO.sub.3 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 [less than or equal to] 0.5. The permittivity-temperature dependences of the (1-x)PbFe.sub.0.5Nb.sub.0.5O.sub.3-xBaFe.sub.0.5Nb.sub.0.5O.sub.3 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 [epsilon](T) curves typical of incipient ferroelectrics and at last, to the step-like frequency-dependent [epsilon](T) curves known for the dielectrics with Maxwell-Wagner-type polarization. The [epsilon] value of BaFe.sub.0.5Nb.sub.0.5O.sub.3 at 20 K measured at 1 MHz does not exceed 30. The character of the evolution of dielectric properties in the (1-x)PbFe.sub.0.5Nb.sub.0.5O.sub.3-x BaFe.sub.0.5Nb.sub.0.5O.sub.3 system and low [epsilon] value of BaFe.sub.0.5Nb.sub.0.5O.sub.3 implies that BaFe.sub.0.5Nb.sub.0.5O.sub.3 is a paraelectric rather than ferroelectric relaxor.