The dielectric properties of zeolites in variable temperature and humidity

Abstract

Measurements are reported of the dielectric response of Na-X, Na-Y and Ca-A zeolites in the frequency range 10 mHz to 10 kHz for a range of humidities and also over a range of temperatures. The extended frequency range compared with earlier studies has enabled a more detailed understanding to be obtained of the low-frequency behaviour, which is dominated by a strongly dispersive dependence on frequency of both the real and the imaginary components of the complex capacitance and has shown the complete absence of proper direct current conduction, contrary to earlier beliefs. The magnitude of the low-frequency behaviour shows an approximately exponential dependence on the water content of the pellets, suggesting that some form of percolation process is determining the low-frequency transport. Strongly non-linear behaviour is seen with respect to the amplitude of the applied voltage signal and this is also responsible for the absence of Kramers–Kronig compatibility in some of the low-frequency data. The observed dielectric spectra are related to the known structural characteristics of the three types of zeolites.