Effects of chemical modification on the electrical properties of 0.67BiFeO₃-0.33PbTiO₃ ferroelectric ceramics

Ceramics of the BiFeO₃-PbTiO₃ solid solution are expected to exhibit interesting ferroelectric and magnetoelectric properties. In this work, chemical modifications are carried out in order to improve the dielectric performance of the materials. Ceramics of 0.67BiFeO ₃-0.33PbTiO₃, 0.67BiFe_0.98Ti _0.02O₃-0.33PbTiO₃ (via B site Ti⁴⁺ modification) and 0.67BiFeO₃-0.33PbTiO₃ sintered under O₂ flow are synthesised. The frequency-dependence of the impedance is measured at various temperatures and analysed. It is found that the dielectric properties are improved by B site Ti⁴⁺ modification and by sintering in O₂ flow. The temperature dependences of dc conductivity of the grains for the three ceramic samples are derived from impedance analysis by fitting their impedance data to an electric equivalent circuit of three RC components. The temperature dependences of both the dc conductivity of the grains and the measured ac conductivity (at high and low frequencies) show that the conductivity for O₂-sintered sample is the lowest, and the conductivity of 0.67BiFe_0.98Ti_0.02O₃-0. 33PbTiO₃ is lower than that of 0.67BiFeO₃-0.33PbTiO ₃. This result is consistent with the dielectric properties of the respective ceramics. The mechanism of the electric conduction is discussed in relation to the chemical modifications and related defect chemistry.