Composition dependence of electrical properties of Al-Te glasses

The electrical resistivity of binary AlxTe100-x glasses of different compos itions (17 less than or equal to x less than or equal to 30), is measured a s a function of temperature in the range 300-180 K. The conductivity activa tion energy (Delta E), estimated from the resistivity variation with temper ature, is found to decrease with increasing Al content and to exhibit a min imum at x = 24 at.% of Al. The initial decrease in Delta E has been explain ed on the basis of the creation of additional positively charged defect sta tes due to the tetrahedral and octahedral coordinations of Al atoms. The pr esence of these additional defect centers causes an upset in the balance be tween the oppositely charged defect states, which subsequently shifts the F ermi level towards the valence band. The increase in activation energy with composition above x = 24 has been attributed to the saturation of these ex tra charged defect states. (C) 1999 Elsevier Science B.V. All rights reserv ed.