The Anelasticity of Natural and Synthetic Quartz at Low Temperatures*

Certain imperfections in alpha-quartz are found to introduce anelastic absorption at low temperatures in crystal resonators. For a shear wave of 5 mc, absorption peaks are observed at approximately 20° and 50°K in unirradiated samples, X-irradiation effects a lowering of the amplitude of the 50°K absorption, while a new absorption is introduced at 100°K. The results of acoustic absorption measurements on a number of selected samples of synthetic quartz resonators suggest that, whereas the 50°K absorption is attributable to excess oxygen, the 100°K defect involves aluminum which is present substitutionally in the crystal structure. X-irradiation-induced lowering of the resonant frequency of crystal resonators is clearly the result of a lowering of the elastic modulus associated with the 100°K anelastic absorption.