Abstract:
Synthetic quartz single crystals are subjected to fracture by a falling load in the temperature range from 20 to 650$^\circ$C (i.e., including the region of the $\alpha\to\beta$ phase transition). The intensity of integrated acoustic emission (AE) generated during the impact is recorded in the frequency range from 80 kHz to 1 MHz. In the temperature range 20–300$^\circ$C and at temperatures above the phase transition temperature (573$^\circ$C), the energy distributions in temporal AE series are correctly described by the exponential function typical of random events, but at 400 and 500$^\circ$C, the energy distributions follow the power law typical of correlated accumulation of microcracks in heterogeneous materials. The temperature effect is explained by the presence of submicrometer inclusions of a vapor–water mixture in the material, which exist as a rule in natural and synthetic quartz single crystals. Upon heating of the material to a certain critical temperature, the internal pressure in the bubbles of liquid attains a value for which the shock wave causes cracking around a large number of uniformly distributed inclusions. As a result, a correlated improper process of accumulation of microscopic defects, which is obviously observed only in heterogeneous materials, evolves in the bulk of deformed quartz heated to 400–500$^\circ$C.
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