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 ∼1 mS cm−1 to <1 μS cm−1 and an increase in bulk activation energy from 0.29 to >1 eV. Plots of permittivity (ϵr) versus temperature for 0.01 ≤ y ≤ 0.05 revealed a step rather than a peak in ϵr 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.