Energy Flux Deviation and Acoustic Attenuation Anisotropy in NaCl1−xBrx Crystals

The energy flux deviation and anisotropy of acoustic wave attenuation in NaCl1−xBrx crystals has been investigated in the frequency range of 30–1200 MHz at room temperature. It is shown that the degree of change in the acoustic attenuation coefficient with increasing bromine content is caused by two factors: decrease in the relaxation time of thermal phonons and increase in the effective Grüneisen constant. All real and imaginary components of the elasticity tensor are determined based on experimental velocity and attenuation coefficient values. The anisotropy of the phase and group velocities of acoustic waves is analyzed, and special directions, along which pure and ordinary acoustic waves propagate, are revealed. A cross-section of the surface of acoustic-wave attenuation coefficient by the (110) plane is constructed for NaCl0.7Br0.3 crystals. It is shown that the highest attenuation anisotropy is observed for quasi-transverse acoustic waves, for which the attenuation coefficients along the [110] and [001] directions differ by an order of magnitude.

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