The electrical properties of Nd‐doped bismuth titanate, Bi4−xNdxTi3O12 (BNT) ceramics prepared by a conventional electroceramic technique have been investigated. XRD analyses revealed Bi‐layered perovskite structure in all samples, and indicated that Bi ions were only substituted near the Ti–O octahedron layers by Nd ions. SEM micrographs show randomly oriented and plate‐like morphology. For the samples with x < 0.5, the current–voltage characteristics exhibit a negative differential resistance behavior, whereas that of the samples with x ≥ 0.5 exhibit a simple ohmic behavior. The conducting filamentary model has been extended and used to explain the negative differential resistance phenomenon in Nd‐doped bismuth titanate ceramics. The P–V hysteresis loop of sample with x = 0.25 were characterized by a large leakage current, and that of samples with x ≥ 0.5 showed the saturated and undistorted hysteresis loops; the remanent polarization (Pr) and coercive field (Ec) of the BNT ceramic with x = 0.5 were above 19 μC/cm2 and 50 KV/cm, respectively. The large value of remanent polarization and low coercive field of Nd‐doped bismuth titanate ceramics promote these materials to potential applications. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Sr2CoNbO6 ceramics were prepared via the solid-state reaction route. The dielectric properties of Sr2CoNbO6 ceramics were investigated as a function of temperature (90–330 K) in the frequency range from 20 Hz to 10 MHz. Our results reveal that the dielectric properties of Sr2CoNbO6 are closely linked with the conductivity of the sample. The conductivity is dominated by hopping localized carriers. The hopping process not only produces considerable conductivity followed the universal dielectric response behavior, but also gives rise to dipolar effects leading to the polaron relaxation in intermediate-temperature range. At low enough temperatures, the hopping process is frozen-in and the low-temperature Maxwell-Wagner relaxation due to frozen carriers featuring the nearly constant loss behavior appears. At higher temperatures, the long-distance transportation of the carriers becomes remarkable. These carriers are easily blocked by various interfaces resulting in space charge therein and the conventional Maxwell-Wagner relaxation in the high-temperature range. Our results demonstrate that a multirelaxation mechanism instead of a single relaxation underlies the colossal dielectric properties of Sr2CoNbO6