Anelastic loss in langatate

Anelastic loss in langatate (La₃Ga_5.5Ta_0.5O₁₄) was measured as a function of temperature from 80 to 1080 K at ultrasonic frequencies from 0.5 to 1.8 MHz. The specimens were monocrystalline cylinders with the trigonal axis parallel to the cylinder axis. Q^-1 and the resonant frequencies were measured with inductive electromagnetic-acoustic and contacting transduction techniques. On cooling from room temperature to 80 K, Q^-1 decreased by approximately an order of magnitude, with the most rapid drop occurring in the 220-260 K range. Part of this temperature dependence may result from the phonon-phonon interaction. However, the frequency dependence of Q^-1 at room temperature is inconsistent with theories for the phonon-phonon interaction, and Qf at room temperature is much lower than values at higher frequencies reported by other researchers. These results suggest that Q^-1 measured at and below room temperature is dominated by an anelastic defect contribution, rather than the intrinsic phonon-phonon damping. Dislocation damping is considered the most likely candidate for this contribution. At elevated temperatures, a relaxation peak appears with a maximum in the 750-810 K range for frequencies between 0.5 and 1.8 MHz. The activation energy of the relaxation is 1.1 eV, which is typical of point-defect relaxations. A second peak appears near 860 K during the first heating and disappears after heating to 1080 K. The observed peaks rise above a background that increases rapidly at the highest temperatures. By analogy with a similar effect observed in quartz, this background is assumed to arise from the anelastic relaxation of diffusing interstitial impurities