“Universal” curve of ionic conductivities in binary alkali borate glasses

Since the discovery of fast ionic conductivity in glasses, there has been a large interest in explaining the diffusion mechanism. With this knowledge one may be able to design new glasses with optimized properties for various applications. It is well known that the ionic conductivity increases rapidly when a network glassformer is modified by the addition of a metal alkali. Despite considerable experimental and theoretical effort, there is currently no consensus regarding the diffusion mechanism [1]. Several models have been proposed: they vary from thermodynamics with principles in models for liquid electrolytes, such as the weak electrolyte model [2], to models based on solid state concepts such as the jump diffusion model [3], the strong electrolyte model [4], and the dynamic structure model [5]. Ionic conductivity σ in glass is a thermally activated process of mobile ions by surmounting a potential barrier EA, of the form: