In this work, the results of measurements of acoustic characteristics (velocities, V, and temperature coefficients of velocities, TCV, for ultrasonic waves with different polarizations) are presented for glasses and glass-ceramics in the lithium aluminosilicate system. It was found that velocities of longitude and shear waves increase monotonously with content of crystal phase. An increase in relative volume fraction of crystals from 10 to 90% in the course of heat treatment leads to change of sign of TCV for longitudinal waves from positive to negative. An anomalous effect of ultrasonic velocity increase with temperature was explained by the static pressure dependence of modulus of elasticity. The reason for pressure change is beliaved to be connected with the temperature-dependence of local microstresses on the boundary of crystalline and glassy phases that have different thermal expansion coefficients (TEC).
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