Internal Friction Tensor in Langasite (LA3Ga5SiO14)
H M. Ledbetter, Sudook A. Kim
Using acoustic spectroscopy, we measured the complete elastic-constant and internal-friction tensor Cy = Cy (1+Q-1y) of langasite, a trigonal-symmetry piezoelectric. To understand the internal friction, we need a mechanism that explains, or is consistent with, six observations: (1) Q-1 (longinudinal) exceeds Q-1 (longitudinal) exceeds Q-1 (traqnsverse); (2) Q-1 is much larger than expected for phonon-phonon interactions; (3)Q-1 varies enormously from crystal to crystal; (4)Q-1 varies with frequency as Q-1 - ω, as predicted for vibrating dislocations or for phonon-phonon interactions; (5) Q-1 does not depend on strain amplitude: (6) Q-1increases with increasing temperature. Phonon scattering by static dislocations provides a possible mechanism, except that the predicted Q-1 magnitude is too small. Phonon scattering by dynamic dislocations provides the best hypothesis.