Charge carrier concentration in ionically conducting glasses was a determining parameter for a meaningful interpretation of processes underlying ionic diffusion in terms of different theories and models. It was suggested that the mobile ion density could be readily calculated from the bias voltage modulation of the space–charge at the metal/glass interfaces. This effect may be modeled by using Mott–Schottky capacitance–voltage characteristics as those encountered in contacts of electronic systems. Conductivity and permittivity spectra of Na2O–0.4Al2O3–2.2SiO2 glasses were measured as a function of temperature and bias voltage showing the electrode polarization effect. It was found that the carrier concentration lay between 3 x 1016 and 4 x 1016/cm3. This was lower, by many orders of magnitude, than the nominal alkali concentration.

Mobile Cation Concentration in Ionically Conducting Glasses Calculated by Means of Mott–Schottky Capacitance–Voltage Characteristics. A.Pitarch, J.Bisquert, G.Garcia-Belmonte: Journal of Non-Crystalline Solids, 2003, 324[1-2], 196-200