Mixed electronic–ionic conductivity in semiconducting CaO–PbO–Fe2O3–P2O5 glasses

Several properties of semiconducting CaO–PbO–Fe2O3–P2O5 glasses have been measured. These properties include density, IR, DSC, and DC conductivity. The change in the structure for the present glasses shows that with increasing CaO content there is a corresponding decrease in the number of Q1 phosphate units and an increase in the non-bridging oxygens (NBOs) as more Q0 phosphate units are formed in the glass. The decrease in the density, d, and glass transition temperature, Tg, is due to the lower degree of cross-bonding between the calcium and NBOs in Q0 phosphate units resulting in a weakening of glass network. The nearly constant DC conductivity and activation energy for glasses containing ⩽12 mol% CaO is attributed to an ion–polaron interaction which is responsible for the low mobility of the calcium ions that shows no detectable contribution to the DC conductivity. With increasing CaO content, up to 24 mol%, the DC conductivity increases which is directly related to an increase in the mobility of the calcium ions. An increase in the number of non-bridging oxygens that appear in the neighborhood of the calcium ions is responsible for an increase in the ionic conductivity.