GREENS FUNCTION APPROACH TO PARALASTIC RELAXATION

The dynamical behavior of the elastic constants of a crystal containing paraelastic defects is investigated theoretically. A two-level model for the paraelastic defect is adopted, and the coupling between the defect and the lattice vibrations is considered to be strong. The imaginary part of the elastic compliance tensor is calculated by the Green's function method using the Feynman graph technique. It is shown that the change of the elastic compliance due to the defects is in general a superposition of the Debye-type relaxation and of resonant absorption of the acoustic waves. Expressions for the linewidth of the resonance and the Debye relaxation time are derived. © 1969 Springer-Verlag.