Ionic Conduction in Phosphate Glasses

Ionic conductivity in phosphate glasses has been known for almost 30 years. Recently these glasses have been shown to exhibit some of the highest ionic conductivities ever reported. In many cases, because of their ease of preparation, low melting points, strong glass-forming character, and simple composition, phosphate glasses have been studied more than any other ionically conducting glasses. However, no single review has ever been made of these glasses with the purpose of correlating the apparent widely disparate values of conductivity that these glasses exhibit. In this review, the conductivities of phosphate glasses are examined considering new structural studies of them. A systematic comparison of the dependence of the conductivity on glass chemistry reveals that, similar to other glass families (silicates and borates for example), the conductivity maximizes when the cation environments in the glass are minimized in their charge density and maximized in their site proximity.