Evolution of dielectric properties in the (1-x) PbFe0.5Nb0.5O3-xBaFe0.5Nb0.5O3 solid solution system

Temperature dependences of the dielectric permittivity epsilon of (1-x)PbFe0.5Nb0.5O3-x BaFe0.5Nb0.5O3 solid solution ceramics at 100Hz-1MHz have been studied in the 12-500K temperature range. To lower the conductivity values and exclude the corresponding relaxations, 1wt% 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 x0.5. T he permittivity-temperature dependences of the (1-x)PbFe0.5Nb0.5O3-xBaFe(0.5)Nb(0.5)O(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 BaFe0.5Nb0.5O3 at 20K measured at 1MHz does not exceed 30. The character of the evolution of dielectric properties in the (1-x)PbFe0.5Nb0.5O3-x BaFe0.5Nb0.5O3 system and low epsilon value of BaFe0.5Nb0.5O3 implies that BaFe0.5Nb0.5O3 is a paraelectric rather than ferroelectric relaxor.