Thermal expansion of amorphous As2S3 at low temperatures

Abstract
The linear expansion coefficient of amorphous As2S3 has been measured from 1·5 to 85 K. The results can be interpreted in terms of a large negative value forthe Grüneisen parameter, γ, associated with tunnelling states as has previously been suggested for vitreous silica and amorphous poly(methylmethacrylate). The large value of γ(∼ – 25) is difficult to explain in terms of the conventional model of tunnelling states, but it is shown that an explanation can be provided by a modification of this model in which the tunnelling entities have to cross broad barriers where the height of the barriers is comparable with the zero-point energy.