CONTROL OF ELECTRICAL-CONDUCTIVITY WITH THE ADMIXTURE OF CHLORINE IN COPPER TELLURITE GLASSES

Copper tellurite glasses containing. CuCI2 with composition 65TeO2-(35-x)CuO-xCuCl2 (mol%) with x=0, 1, 2, 3, 4, 5 were prepared by quenching the melt. An increase in density with the addition of CuCl2 and with a corresponding decrease in molar volume, has been observed. The d.c. conductivity of copper tellurite glasses is found to be very sensitive to the reduced valency ration C=[Cu+]/[Cutotal] and depends on the relative concentrations of Cu+ (reduced valency state) and Cu2+ (higher valency state) ions. It is found that by adding cupric chloride to the melt when the glass is formed, the chlorine in the salt which acts as an oxidizing agent alters the ratio of the concentrations of Cu+ and Cu2+ ions in the glass and hence the conductivity. It is found that more than 2 mol% of cupric chloride reduces the conductivity very sharply due to the formation of chlorine clusters in the form of local TeCl2+ whereas less than 2 mol% of CuCl2 leads to an increase in conductivity due to the Cu+→Cu2+ transition which is negligibly affected by the chlorine due to the formation of TeCl2 which is amorphous in nature. The increase and decrease of electrical conductivity of glasses containing less or more than 2 mol% CuCl2 is also interpreted in terms of the electronic transitions between the orbitals of tellurium 3d electrons, their binding energies and peak widths on the basis of XPS (X-ray Photoelectron Spectroscopy) study, and it was found that the increase in bandwidth supports the idea of clustering of chlorine above 2 mol% CuCl2 and causing a decrease in the conductivity. Overall the conductivity is found to be somewhat uncontrollable in these glasses because it is not simply dependent on the concentration of Cu2+ ions. © 1990 Chapman and Hall Ltd.