Abstract
A commercial automatic impedance analyser was used to obtain complex impedance data for obsidians from Taupo, New Zealand, over an ac frequency range of 5 Hz-13 MHz. The results were analysed in the impedance and electric modulus formalisms, both in the complex plane and as spectra, yielding information on a number of electric field relaxation processes within the glass: ion transport in bulk glass, in charge-carrier depleted glass, and in microcrystals, and a Maxwell-Wagner type interfacial polarisation. Differences between the Arrhenius behaviour of relaxation and conductance in the charge-carrier depleted layer are discussed in terms of the weak electrolyte theory of conduction in glass. Glasses of differing physical appearance from the same eruptive centre had the same bulk glass structure with conductivity σ = (20 ± 8) exp (− 74 kJ mol −1/ RT)S cm −1 for 150°C < T < 650°C.
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