Low-temperature thermal expansion of disordered solids

Abstract

The thermal-expansion coefficients $\alpha$ of vitreous silica, neutron-irradiated vitreous silica, vitreous silica containing O${\mathrm{H}}^{-}$ or ${\mathrm{K}}_2$O, the amorphous polymers SC5 (Scotchcast 5 epoxy, 3M Company) and PMMA, (polymethylmethacrylate) the chalcogenide glass ${\mathrm{As}}_2$ ${\mathrm{S}}_3$, glassy PdSiCu, and crystalline samples of Na $\beta$-alumina and Zr${\mathrm{O}}_2$:${\mathrm{Y}}_2$ ${\mathrm{O}}_3$ have been measured to temperatures $T\lesssim 1$ K. The low-energy excitations generally found in glassy materials influence or dominate $\alpha$ at $T<\mathrm{}1\mathrm{}$ K. However, unlike the specific heat and other properties, $\alpha$ is not a universal property of glasses. The $\alpha$ associated with the excitations may be large or small, positive or negative. The results may be explained provided the excitations exhibit a broad spectrum of deformation potentials in addition to a broad spectrum of energies.