Effect of humidity on the dielectric constant and electrical impedance of mesoporous zirconia ceramics

The effect of humidity on the dielectric constant and electrical impedance of porous 8 mol% yttria stabilized zirconia ceramic is examined. Samples with pore volume fractions from 33% to 55% were prepared from a fine powder by uniaxial pressing and firing. Measurements, in different relative humidities from <3% to 100%, showed a strong increase of dielectric constant with water content of the unfired and fired porous ceramics. The dielectric constant can be described with good agreement to experimental values using a 2 step model involving the Hashin-Shtrikman upper bound and Landauer’s effective medium relation, analogous to the behavior of thermal conductivity. Water is assumed to be located as a layer of variable thickness on the interior solid surfaces of the pores. A.c. impedance measurements also reveal a short circuit of insulating dielectric behavior at higher water contents, interpreted as surface conduction of protons.