A unified superionic theory of the photoinduced and thermally activated dark diffusion of silver in the chalcogenide glasses

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Abstract
A unified superionic diffusion theory of the photoinduced and the thermally activated dark diffusion of silver in chalcogenide glasses is presented. The theory is based on the proposition that the activation energy for the diffusion of silver in the glasses consists of the following two components: (a) an activation energy for the ionization of deep donor-like interstitial silver impurities, which can be supplied either thermally or through the impurity-induced absorption of photons, and (b) a small, superionic thermal activation energy for the ambipolar diffusion of the ionized impurities. A model for the interfacial reaction through which the initially physically adsorbed silver gains entry into the glasses is also proposed. It is argued that the superionicity which is proposed to underlie photodoping differs in fundamental ways from superionicity encountered in the well known prototype silver superionic conductors, namely, α-Ag2 S and α-AgI.