Velocity and Attenuation of Acoustic Waves in Y3Al5O12 Crystals at High Temperatures

The temperature dependences of the velocity and attenuation coefficient of longitudinal acoustic waves in pure and neodymium-doped yttrium–aluminum garnet (YAG) crystals have been studied in the temperature range of 290–450 K using the Williams–Lamb ultrasonic method at a frequency of 30 MHz. The temperature coefficients of the elastic constants c₁₁^' and c₄₄^' in these crystals were determined. It is shown that the attenuation of acoustic waves significantly changes in the investigated temperature range, especially in doped YAG crystals. It is found that, in the case of longitudinal acoustic waves, the maximum deviation of the energy flux from the wave vector is 0. 8° for pure crystals and 2. 8° for neodymium-doped crystals. Based on the measured values of the velocity and attenuation of acoustic waves, the real and imaginary components of the elasticity tensor were determined; this data make it possible to determine the velocity and attenuation coefficient of acoustic waves along any arbitrary direction in crystals.