Humidity-dependent impedance in porous spinel nickel germanate ceramic

The spinel ceramic material nickel germanate, Ni2GeO4,has been found to exhibit a humidity-dependent impedance. A change in the magnitude of the impedance at 100 Hz, from 10(8) Omega at 20% R-H to 10(4) Omega at 98% R-H, at 298 K, is typical. The effect of frequency on the complex impedance has been investigated over the frequency range 10 mHz-10 MHz, using the technique of impedance spectroscopy. The observed impedance spectra show two regions, indicative of an ionic-charge transport process and a charge transfer to the electrodes, suggesting that at high levels of humidity conduction is essentially electrochemical. (C) 1998 American Institute of Physics. [S0003-6951(98)02423-1].