Double-perovskite Ca 2 CoNbO 6 (CCNO) ceramics were prepared via the solid-state reaction route. Their dielectric properties were investigated as a function of temperature (between 100 and 330 K) in the frequency range from 40 Hz to 10 MHz. Two thermally activated dielectric relaxations were observed with the activation energy around 0.13 eV for the low-temperature relaxation and 0.37 eV for the hightemperature relaxation. Annealing in O 2 and N 2 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.
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