Abstract
The dielectric constant ɛ and loss tangent tanδ of Sr3CuNb2O9 perovskite ceramics prepared by solid-state reactions have been measured at temperatures from 300 to 900 K and frequencies from 25 to 1 × 106 Hz. The results demonstrate that the samples slowly cooled from the temperature of the final, high-temperature firing (1200°C) have relatively low permittivity (ɛ ≃ 10) and dielectric losses (tanδ ≃ 0.005 at 1 kHz) at room temperature, with no strong dielectric dispersion and no prominent maxima in the temperature dependences of their permittivity and dielectric loss. The ceramics quenched from 1300°C exhibit a pronounced Debye-type low-frequency relaxation and strong dielectric dispersion in conjunction with high permittivity ɛ ≃ 2000 at low frequencies and/or high temperatures. The observed dielectric anomalies in the Sr3CuNb2O9 ceramics can be understood in terms of Maxwell-Wagner relaxation at dielectric inhomogeneities associated with the quenching-induced difference in oxygen-vacancy concentration between the grain bulk and surface layer.
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