Mobile cation concentration in ionically conducting glasses calculated by means of Mott–Schottky capacitance–voltage characteristics

Charge carrier concentration in ionically conducting glasses is a determining parameter for a meaningful interpretation of processes underlying ionic diffusion in terms of different theories and models. We suggest that mobile ion density can be readily calculated from the bias voltage modulation of the space–charge built 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. We found that carrier concentration lies within the range 3–4 × 1016 cm−3 which is lower by many orders of magnitude than the nominal alkali concentration.