Dynamic Viscoelasticity of Glasses in the Systems As-S and As-Se

Abstract

Dynamic viscoelasticity of glasses in the systems As-S and As-Se was measured by a method of forced torsional vibration with dynamic modulus approximately from 1010 to 108 dyne/cm2. The dispersions of dynamic elasticity (G′) and dynamic loss (G″) with temperature (ω=0.26rad/sec) for the glasses with As content at 40 atomic per cent in the both systems As-S and As-Se appeared at the highest temperature in the same system. However, the viscoelastic behavior which is represented by the change of G′ and G″ appeared even near the fixed temperature Tf, which is the temperature of isoviscosity η=2×1013 poise, when S or Se content became above 80 atomic per cent.Frequency-temperature superposition of each run for all samples was successful in this range. And so, at Tf of each sample we could draw master curves as shown in Fig. 6 and 7. As to the shift factor, aT, log aT vs. 1/T plots give essentially a straight line for each sample as shown in Fig. 8. Therefore, for the dynamic viscoelastic relaxation of glass, the apparent activation energy can be calculated by the following equation, ΔH=Rd (log where R is the gas constant. The results are shown in Fig. 9. aT)/d(1/T), In the As-S system, the activation energy is about 70kcal/mole at As2S3 (As 40atom%) and it decreases gradually with increasing S contents. But it shows an unusual maximum around As2S8 (S 80atom%). On the other hand, in the As-Se system, the activation energy is about 65kcal/mole at As2Se3 (As 40atom%) and decreases with increasing Se content. However, it increases again with Se content above 80 atomic per cent.The distribution of relaxation time can be expressed approximately by the following formula, dG′(ω)/dlogω=ψL(log τ). The results are shown in Fig. 10. The distribution curves for all the samples go through the maximum. The peak appears at the longest period at As2S3 and As2Se3 (As 40atom%) in As-S and As-Se systems, respectively, and shifts to shorter period with increasing S and Se contents.