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Mixed electrical conduction in a hydrous pantellerite glass

2012; Elsevier BV; Volume: 320-321; Linguagem: Inglês

10.1016/j.chemgeo.2012.05.023

1872-6836

Brent T. Poe, Cláudia Romano, Danilo Di Genova, Harald Behrens, Piergiorgio Scarlato,

Geological and Geochemical Analysis

Abstract Electrical conductivity measurements were carried out on pantelleritic trachyte glasses containing up to 3.5 wt.% dissolved H 2 O. At temperatures below about 700 K, we find evidence for small polaron conduction due to the presence of both ferrous and ferric iron in the glass. At the higher temperatures of the investigation (up to 973 K), a marked change in the conductivity–temperature relation is observed, which suggests that an ionic conduction mechanism becomes the dominant means of charge transport. In the ionic conduction regime, conductivity increases with increasing H 2 O concentration. Activation energies are similar for both the anhydrous and hydrous glasses, indicating that the conductivity is controlled by sodium diffusion even for the highest H 2 O concentration examined. A slight variation in activation energy is observed depending on the H 2 O concentration, which is most likely associated with the depolymerising effect of dissolved water on the silicate network structure. At low temperatures, we find a dramatic effect of fO 2 on the conductivity that supports an electronic conduction mechanism based on small polaron hopping between Fe 3+ and Fe 2+ sites. This electronic pathway controls the overall electrical conductivity in these alkali-rich glasses at temperatures exceeding 500 °C if conditions remain anhydrous at an oxygen fugacity of 0.2 atm.