Electrical Parameters of SnO₂ Based Varistor Ceramics with CaO and BaO Additions

Abstract

In the tested SnO2-Co3O4-Nb2O5-Cr2O3-CuO varistor ceramics the adding of CaO or BaO oxides leads to the decrease of the electric conductivity in the low electric field and correlated increase of the potential barrier height at the SnO2 grain boundaries (from 0.7 to 1.0 eV). The coordinated changes of electrical parameters with the increase of the burning temperature from 1520 to 1620 К (the increase of the linear shrinkage, a grain size, an electric conductivity, a nonlinear coefficient , a normalized nonlinear coefficient , a dielectric permittivity and the decrease of the qualifying electric field E1, an activation energy of electric conduction and a grain specific resistance) prove the barrier mechanism of electric conductivity in the SnO2 based ceramics. The highest data and = 0.02 cm•V-1 has ceramics with CaO addition baked at 1620 K. According to the impulse experimental data in the high electric field the increase of burning temperature causes the increase of SnO2 grain average size and the decrease of their grain specific resistance . The obtained value = 1.1 Ohm•cm for SnO2-Co3O4-Nb2O5-Cr2O3-CuO ceramics is the lowest among those found in SnO2 based ceramics. The addition of CaO or BaO increase the grain specific resistance and decrease their average size. Key words: varistor, SnO2, ceramics, grain boundary, CaO, BaO, electric conductivity, specific resistance, grain size.