EFFECT OF HALIDE-IONS ON THE ELECTRONIC CONDUCTIVITY IN CALCIUM BORATE GLASSES

Some halogen-doped calcium borate glasses containing iron have been prepared according to the percentage molar composition [(30 - x) CaO . x CaX2 . 10 Fe2O3 . 60 B2O3] and annealed. It is found that the conduction in the semiconducting glasses is mainly due to electronic conduction. The results show that the halide ions may be introduced as modifiers for CaX2 concentration < 10 mol% (X = F, Cl, and Br) but they are network formers at CaX2 > 10 mol%. It is proposed that at 10 mol% the network structure for all glasses seems to be the same. The dependence of resistivity on the halide ions concentration as well as the slight variation of activation energies, could be explained on the basis of electron-lattice interaction. Mathematical expressions for fitting and describing the dependence of resistivity on CaX2 concentration are deduced and formulated by the following equations: rho = rho0 exp [+/- ac(1 - bc)] and rho = rho10 exp [+/- a'c(1 - b'c)] for the two regions around the critical concentration.