JOURNAL OF MATERIALS SCIENCE 19 (1984) 1563-1567 The control of the electrical conductivity of germanium vanadate glasses by the admixture of chlorine during preparation A. A. KUTUB Department of Physics, Umm-AI-Qura University, Makkah Al-Mukaramah, Saudi Arabia M. N. KHAN, E. E. KHAWAJA Department of Physics, University of Petroleum and Minerals, Dhahran, Saudi Arabia C.A. HOGARTH Department of Physics, Brunel University, Uxbridge, Middlesex, UK The electrical conductivity of germanium vanadate glasses depends on the relative concentrations of V 4+ and V s+ ions. It is found that by adding VCI3 to the melt when the glass is formed, the added chlorine which acts as an oxidizing agent alters the ratio of concentration of vanadium ions and thus the conductivity. The optical absorption coefficients and d.c. conductivities of germanium vanadate glasses are measured as functions of VCl 3 content. It is found that the activation energy for conductivity increases with chlorine content, the increase of the activation energy corresponding to the change in optical gap energy. It is considered therefore, that the principle of the addition of a strong oxidizing agent to the glass to alter the reduced valency ion ratio may have general application in the control of electrical conductivity in transition metal ion glasses. 1. Introduction Oxide glasses containing transition metal ions were first reported in 1954 [1]. Several transition metal oxides when heated with glass-forming substances such as P~Os, TeO2 and GeO2, form glasses on quenching from the melt. The loss of oxygen from the melt produces lower valency transition metal ions. Electrical conduction in these glasses occurs by electron hopping from an ion of the low valency state (V 4+) transition metal to an ion of the high valency state (V s§ [2]. Murawski et al. [3] have suggested that although the thermal activation energy for conduction appears to be the dominating factor which con- trols the conductivity, it has recently been shown [4] that the admixture of chlorine has a great influence on the conductivity has been shown to be related to the ratio and relative concentrations of the ions in the different valency states (Mott [5], Linsley/et al. [6], Moridi and Hogarth [7]). The electrical conductivity of these glasses is sensitive to the ratio (V+)/(Vtota~) where (Vtotal) represents the total concentration of vanadium in glass [5]. It is found that a maximum in the electrical conductivity of such glasses is observed for sample in which the concentrations (V 4+) and (V s§ are of the same order of magnitude. For this reason a method which could control the value of (V 4+) is of great importance in controlling the conductivity of the glasses. In general , glassy and amorphous materials cannot be doped to desired values of conductivity by the addition of small amounts of donors or acceptor impurities as in the normal procedure for crystalline semiconductors. We report here a pro- cess for the control of the electrical conductivity of vanadate glasses containing a fixed proportion of vanadium. 0022--2461/84 $03.00 + .12 9 1984 Chapman and Hall Ltd. 1563