Ceramics International 30 (2004) 1435–1442 Effects of chemical modification on the electrical properties of 0.67BiFeO 3 -0.33PbTiO 3 ferroelectric ceramics W.M. Zhu, Z.-G. Ye ∗ Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC, Canada V5A 1S6 Received 3 December 2003; received in revised form 18 December 2003; accepted 23 December 2003 Available online 10 May 2004 Abstract Ceramics of the BiFeO 3 -PbTiO 3 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 -0.33PbTiO 3 , 0.67BiFe 0.98 Ti 0.02 O 3 -0.33PbTiO 3 (via B site Ti 4+ modification) and 0.67BiFeO 3 -0.33PbTiO 3 sintered under O 2 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 Ti 4+ modification and by sintering in O 2 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 O 2 -sintered sample is the lowest, and the conductivity of 0.67BiFe 0.98 Ti 0.02 O 3 -0.33PbTiO 3 is lower than that of 0.67BiFeO 3 -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. © 2004 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: B. Spectroscopy; B. X-ray method; C. Electrical conductivity; C. Dielectric properties 1. Introduction The (1 - x)BiFeO 3 –xPbTiO 3 solid solution of perovskite structure with compositions near the morphotropic phase boundary (MPB) (x = 0.3–0.35) shows a huge tetragonality (lattice parameter ratio c/a) in its tetragonal phase [1–3], which theoretically predicts large electric polarisation [3]. The ferroelectric Curie point of the MPB compositions derived from high temperature X-ray diffraction is around 700 ◦ C [4], indicating the potential of this system for high temperature applications using piezo- and ferroelectric properties. Experimentally, due to high electric conductiv- ity [3,4], the dielectric constant of this system can only be measured at high frequencies and at temperatures lower than 500 ◦ C [4], or with the aid of a special technique of ultrahigh frequency measurement [2], and no data on the electric polarisation were reported. On the other hand, little work has focused on the electric conduction study for this ∗ Corresponding author. Fax: +1-604-291-3765. E-mail address: zye@sfu.ca (Z.-G. Ye). system. The only conductivity measurement on ceramic sample [4] showed that the dc conductivity of the MPB composition is only one order of magnitude higher than that of PbTiO 3 ceramic, which is lower than expected from the dielectric results of the (1 - x)BiFeO 3 –xPbTiO 3 ceramics. So it is interesting to study the electric conduction behaviour in this system, which will be helpful for improving the dielectric properties by decreasing the electric conductivity of this system. Aliovalent doping and annealing (or sinter- ing) in a certain atmospheric environment are commonly used to modify the conductivity by changing the concentra- tion of conduction species [5]. Being an ionic compound, the BiFeO 3 –PbTiO 3 solid solutions may have high energy gap between valence band and conduction band, so that electrons could not be thermally activated easily in the tem- perature interval of measurement (≤550 ◦ C in our case). Therefore, the conductivity in this system is expected to result mainly from the presence of defects, which introduce extrinsic (donor and/or acceptor) levels allowing electrons to be thermally activated. In this work, we use chemical modifications to change the concentration of some defects in the ceramics. The dielectric properties and electric con- 0272-8842/$30.00 © 2004 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2003.12.072