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Electrical and Dielectric Properties of Isostatically Pressed Alumina-Based Electroporcelain

V. Trnovcová, M. Kubliha, I. Štubňa, Š. Csáki, Š. Csáki

Journal of Ceramic Science and Technology, Vol. 9, No. 2 (2018), pp. 149-154

DOI: 10.4416/JCST2017-00089

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Abstract

The anisotropy of dc and ac conductivities and relative permittivity is studied in green, dehydroxylated, and fired, cold-isostatically pressed alumina-based electroporcelain. The dc conductivity, σdc, of green samples is isotropic and its temperature dependence contains two Arrhenius-like sections: below 140 °C, σdc = 5·10-2exp (-0.77/kT), and from 150 to 400 °C, σdc = 4·10-4exp (-0.56/kT), where σdc is in S/cm and conduction activation energies are in eV. The dc conductivity of dehydroxylated samples is also isotropic but much lower: below 200 °C, σdc = 1.7·10-3exp (-0.8/kT); above 210 °C, σdc = 0.7exp (-1.07/kT). Fired samples behave as fast-ionic conductors, above 300°C; temperature dependences of both dc and ac conductivities, in both directions, are given as σ = 17 exp (-0.785/kT). The anisotropy of the ac conductivity and permittivity is distinct only in as-received samples, being higher in the samples with a rotational axis in the direction of the blank radius. In green samples, anisotropy of the ac conductivity and permittivity is observed owing to relaxation of water molecules in closed pores and capillaries. The static relative permittivity of dehydroxylated and fired samples is equal to 6.3 ± 0.3 or 6.9 ± 0.1, respectively.

Keywords

Electrical conductivity, dielectric properties, alumina-based electroporcelain, cold isostatic pressing

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