Analysis of the admittance-frequency and capacitance-voltage of dense SnO2•CoO-based varistor ceramics

This article describes the admittance-frequency feature of a class of SnO2.CoO-based polycrystalline ceramics with high nonlinear current-voltage characteristics (nonlinear coefficients above 50). Broad relaxation peaks caused by the presence of deep trap states were characterized based on the admittance response of different systems doped with La2O3, Pr2O3, and CeO2. The calculation of the energy of this deep trap level revealed not only that all the compositions share the same value but also that this value could be attributed to an oxygen vacancy or to Co-Sn(') like defects. The values of barrier height and density of states obtained from a capacitance-voltage analysis are in good agreement with the nonlinear coefficients. The highest nonlinear coefficients are found in compositions with greater barrier height values and higher density of deep trap states at the grain boundary interface. (C) 2002 American Institute of Physics.