The studies of crystalline ionic conductors where excess ions were provided by point defect continued through 1950s, and the specific mechanism of conduction was established for each compound depending on its ionic structure. The emergence of glassy and polymeric electrolytes in the late 1970s provided new ionic conduction mechanisms. A relatively wide range of conductivities was attained in glasses, wherein mobile ions were dynamically decoupled from the matrix. It was found that the conductivity could be increased by doping a glass with certain salts, or by using a glass mixture. The conductivity values could be as high as 0.03 S/cm at room temperature, with activation energies as low as 20 kJ/mol. Compared to crystals, glasses have isotropic properties, continuously tunable composition and good workability; they lack the detrimental grain boundaries and can be molded into any shape, but understanding their ionic transport was complicated by the lack of long-range order.
Historically, an evidence for ionic conductivity was provided back in the 1880s, when German scientists noticed that a well-calibrated thermometer made of Thuringian glass would show −0.5 °C instead of 0 °C when placed in ice shortly after immersion in boiling water, and recover only after several months. In 1883, they reduced this effect 10 times by replacing a mixture of sodium and potassium in the glass by either sodium or potassium. This finding helped Otto Schott develop the first accurate lithium-based thermometer. More systematic studies on ionic conductivity in glass appeared in 1884, but received broad attention only a century later. Several universal laws have been empirically formulated for ionic glasses and extended to other ionic conductors, such as the frequency dependence of electrical conductivity σ(ν) – σ(0) ~ ν, where the exponent p depends on the material, but not on temperature, at least below ~100 K. This behavior is a fingerprint of activated hopping conduction among nearby sites.