Charge carrier concentration in glasses. dependence on composition

Admittance spectra of the ion conducting glasses xNa₂O(1−x)SiO₂ and xK₂O(1−x)SiO₂,(x=0,1–0,3) have been studied on small signal conditions from room temperature to 713 K. Conductivity relaxation in the bulk and space charge relaxation due to drift and diffusion near the electrodes were found in separated parts of the frequency range 10⁻⁴–10⁶ Hz. The data show Arrhenius behaviour for dc conductivity and conductivity relaxation. The determination of the charge carrier concentration is based on the analysis of the beginning of space charge relaxation. The free carrier concentration, n₀, were evaluated to be of the order of 10²³ m⁻³ at temperatures 400 – 700 K and show a weak dependence on composition. The dominant factor determining conductivity was mobility in these glasses. The strong temperature dependence of n₀ below 400 K indicates changed conditions for the development of the space charge relaxation which are discussed. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11–18 Sept. 1994.