The scattering of lattice vibrations by a point defect: I

A simple derivation is given of the relaxation time for the scattering of phonons by an `isotopic' impurity in a crystal. A method of applying the result to realistic crystal models is given, and this is related to the analytic formulae derived by other workers. The case of scattering by iodine ions substituted in KCl is used as an illustration throughout. Implications for thermal conductivity in this system are discussed and a comparison is made with experiment. It is shown that the method may be easily applied to scattering by more complicated impurity centres.