Normal process relaxation times from thermal conductivity data

It is shown that, if thermal phonons are scattered by both processes which conserve and also by those which do not conserve wave number, then the thermal conductivity K may be expressed as a power series of the form

Here τ, C, v and α are respectively the relaxation time for normal processes, the specific heat, the phonon velocity and a numerical constant. K₀ is inversely proportional to the strength of those processes which do not conserve wave number and hence, by measuring experimentally how K varies with the strength of these processes, the value of τ may be found. The method is applied to lithium fluoride giving results which are in reasonable agreement with those obtained in earlier work by more complicated analysis.