Ti-Doping to Reduce Conductivity in Bi0.85Nd0.15FeO3 Ceramics

In 2009, Karimi et al. reported that Bi1-xNdxFeO3 0.15 <= x <= 0.25 exhibited a PbZrO3 (PZ)-like structure. These authors presented some preliminary electrical data for the PZ-like composition but noted that the conductivity was too high to obtain radio-frequency measurements representative of the intrinsic properties. In this study, Bi0.85Nd0.15Fe1-yTiyO3 (0 <= y <= 0.1) were investigated, in which Ti acted as a donor dopant on the B-site. In contrast to the original study of Karimi et al., X-ray diffraction (XRD) of Bi0.85Nd0.15FeO3 revealed peaks which were attributed to a mixture of PZ-like and rhombohedral structures. However, as the Ti (0 < y <= 0.05) concentration increased, the rhombohedral peaks disappeared and all intensities were attributed to the PZ-like phase. For y = 0.1, broad XRD peaks indicated a significant decrease in effective diffracting volume. Electron diffraction confirmed that the PZ-like phase was dominant for y <= 0.05, but for y = 0.1, an incommensurate structure was present, consistent with the broadened XRD peaks. The substitution of Fe3+ by Ti4+ decreased the dielectric loss at room temperature from >0.3 to <0.04 for all doped compositions, with a minimum (0.015) observed for y = 0.03. The decrease in dielectric loss was accompanied by a decrease in the room temperature bulk conductivity from similar to 1 mS cm(-1) to < 1 mu S cm(-1) and an increase in bulk activation energy from 0.29 to >1 eV. Plots of permittivity (epsilon(r)) versus temperature for 0.01 <= y <= 0.05 revealed a step rather than a peak in epsilon(r) on heating at the same temperature determined for the antiferroelectric-paraelectric phase transition by differential scanning calorimetry. Finally, large electric fields were applied to all doped samples which resulted in a linear dependence of polarisation on the electric field similar to that obtained for PbZrO3 ceramics under equivalent experimental conditions.