Optical studies of the thermal dissociation of OH - ion aggregates in MgO

Abstract

Abstract The thermal dissociation of two OH − ion aggregate centres has been studied through the decay of the associated optical absorption bands. The first of the centres studied, with an absorption band at 3296 cm −1 , has been shown to consist of an OH − ion in association with a magnesium vacancy (1), the (OHV) centre. The second (absorption band at 3310 cm −1 ) is an (OHV) centre in association with a trivalent impurity ( I )[2]. We term this the (OHVI) centre. Over the temperature range 470°–620°C the decays take a simple form, predicted by rate theory. From these measurements, and new data on the equilibrium concentration of the centres as a function of temperature, the dissociation activation energy (1.43 eV), the binding energy (⪆FG 0.23 eV) and the association activation energy (⪅ 1.20 eV) of the (OHV) centre are found, together with the binding energy of the trivalent impurity I to the (OHVI) centre (84 meV).