C.C. Wang

Low-temperature dielectric properties of double-perovskite Ca2CoNbO6

Double-perovskite Ca2CoNbO6 (CCNO) ceramics were prepared via the solid-state reaction route. Their dielectric properties were investigated as a function of temperature (between 100 and 330xa0K) in the frequency range from 40xa0Hz to 10xa0MHz. Two thermally activated dielectric relaxations were observed with the activation energy around 0.13xa0eV for the low-temperature relaxation and 0.37xa0eV for the high-temperature relaxation. Annealing in O2 and N2 can remarkably change the dielectric constant, background, relaxation peak intensity and position, etc. These results can be well explained based on the fact that both oxygen and cobalt vacancies coexist in the sample. The low-temperature relaxation was found to be related to the dipolar effect due to the hopping holes, and the high-temperature relaxation was associated with the defect relaxation caused by oxygen and cobalt vacancies.

Relationship between the dielectric properties and the conductivity of Ba2FeNbO6

In the present work, we performed detailed investigation on the relationship between the dielectric properties and the conductivity of Ba2FeNbO6. Our results revealed that (1) the colossal dielectric behavior of the sample can be well understood based on the framework of universal dielectric response, (2) the observed relaxation shows a distinct deviation from the Arrhenius behavior, and (3) the peak intensity of dielectric loss can be well expressed by a relation similar to the Fermi–Dirac distribution function rather than a thermally activation relation. These are the typical features for the hopping motions of polaronic carriers demonstrating that the dielectric properties and the conductivity of Ba2FeNbO6 are closely linked.