HUMIDITY-DEPENDENT IMPEDANCE IN POROUS SPINEL NICKEL GERMANATE CERAMIC

The spinel ceramic material nickel germanate, Ni2GeO4,has been found t o 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 a t 98% R-H, at 298 K, is typical. The effect of frequency on the comple x impedance has been investigated over the frequency range 10 mHz-10 M Hz, using the technique of impedance spectroscopy. The observed impeda nce spectra show two regions, indicative of an ionic-charge transport process and a charge transfer to the electrodes, suggesting that at hi gh levels of humidity conduction is essentially electrochemical. (C) 1 998 American Institute of Physics. [S0003-6951(98)02423-1].