Near 35°K the internal friction of vitreous silica reaches a peak value which increases with frequency. The temperature curves of the torsion and Young's moduli are concave upward with minima near 65°K and are independent of frequency. These effects are reversible with temperature. Their cause cannot be the usual type of relaxation process or anything involving diffusion or large amounts of shear.

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An acoustic relaxation effect occurs near 40°K in Nio.75Fe2.25O4 and is attributed to a stress-induced change in distribution of Fe ++ and Fe +++ similar to that occurring in magnetite. The process involves electron diffusion. The activation energy is between 0.026 and 0.055 ev per electron jump.