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The glass transformation (Tg) and onset crystallization temperatures (Tx) of (100 − x) TeO2–(x)V2O5, (x ⳱10, 35, and 50 mol%) glasses were measured in the temperature range 300–800 K by differential scanning calorimetry at different heating rates. From the variation of the heating rate, the glass transition activation energy was calculated by different methods. The glass stabilization range S ⳱ Tx − Tg was calculated for the whole glass series. Quantitative analysis of the glass transformation temperature was carried out using the calculated number of bonds per unit volume and oxygen packing density.

I. INTRODUCTION

Early research (1973) showed that vanadium tellurite glasses were semiconducting and that they switched when a high electrical field was applied.1–4 Also, it has been reported that these glasses are highly conductive compared with vanadium phosphate glasses or other glasses containing transition metal oxide with the same amount of charge carriers.2,3 Previously, both electrical conductivity and dielectric constant of pure and binary tellurite glasses were measured and analyzed in detail.5–7 Recently, in 1998, direct experimental evidence for the electrothermal origin of nonohmic behavior on V2O5– TeO2 glasses was achieved.8 Due to the importance of the binary glass system TeO2–V2O5, two ultrasonic properties, velocity and attenuation, were measured to find the role of V2O5 in the glass network.9,10 Previously, the thermal properties—thermal expansion coefficient and glass transformation temperature, devitrification, and vitrification—were measured for binary rare earth and transition metal tellurite glasses.11,12 The specific heat capacity Cp of noncrystalline solid TeO2–V2O5 glasses was measured in the temperature range 300–650 K.13 The difference of specific heat capacities ⌬Cp of the glass (Cpg) and supercooled liquid (Cpl) at Tg was also measured for a series of binary vanadium tellurite glasses.13 Also, the ratio (Cpg /Cpl) was calculated for the present glass series, TeO2–V2O5. The physical properties of tellurite glasses were calculated and published.14 The goal of the present study was to measure the glass transformation and onset crystallization temperatures, to calculate the glass transformation energy, and to find the glass stability of these semiconducting vanadium tellurite

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J. Mater. Res., Vol. 18, No. 2, Feb 2003 Downloaded: 21 Jan 2015

glasses. The above thermal properties and the nonbridging oxygens (NBO) are very important in understanding the electrical behavior of semiconducting noncrystalline tellurite glasses because the hopping process of conduction in noncrystalline solids depends mainly on the temperature and NBO. II. EXPERIMENTAL A. Glass preparation, vitreous state confirmation

The binary glass system (100 − x)TeO2–(x)V2O5 was prepared by mixing all specified weights of tellurium oxide (TeO2, 99.0% purity) and vanadium oxide (V2O5, 99.5% purity), where x ⳱10, 35, and 50 mol%. The mixing process took