Relaxation effects in glassy selenium

Abstract

Thermal relaxation phenomena were measured in samples of both melt-quenched and evaporated selenium. On the basis of earlier studies, the two methods of preparation produced samples with polymeric chain concentrations of 30–50% and 0% respectively; the rest of the material was in the form of eight member rings. The relaxation peak occurred between 320 and 330 K, and had an activation energy of ≈22.5 kcal/mole for the melt-quenched sample. A decrease of 1 K in the glass relaxation temperature and 0.5 kcal (a at) −1 in the activation energy was observed in samples which had been initially evaporated. No change was observed as a result of melting and quenching these evaporated samples. It is postulated that there was no change when the evaporated sample was melt-quenched be because rings and chains can interconvert and equilibrate relatively readily at temperatures as low as T g (50° C), and consequently the samples all had the same structure after once being heated above T g. The differences observed are probably due to accidental impurities in the evaporated samples which help catalyze the interconversion of rings and chains. Further, since the equilibrium concentration of polymeric chains is temperature dependent, it is postulated that the large relaxation effects seen at T < T g are due to the equilibration of these chains with the rings. The observed activation energy for the relaxation supports this view. It is about the same energy as has been previously measured for Se 8 ring breaking in liquid selenium. Two consequences of this postulate are that the selenium analog to the sulfur polymerization transition must occur well below room temperature if it exists, and therefore, that the equilibrium ring-chain ratio can be smoothly extrapolated down to room temperature from the published high-temperature data.