Hypersonic Attenuation in Rutile

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Abstract
The low-temperature frequency and temperature dependence of the microwave acoustic attenuation in rutile is determined. In the temperature region where three-phonon interactions dominate the attenuating process, a decided anisotropy and mode dependence is observed in the attenuation of the induced acoustic phonon. Parameters used in the description of the attenuation, such as the phonon lifetimes, should reflect this anisotropy rather than a spatial average. The introduction of low densities of imperfections by vacuum reduction of the rutile has no appreciable effect on the low-temperature frequency and temperature dependence of the attenuation. The phonon interactions leading to the attenuation appear to be homogeneous and reflect the anharmonic components of the crystal potential rather than any microscopic inhomogeneities.