Phonons are scattered in the crystal at impurity centers with a scattering cross section s of the geometric order (10-15 cm2). Estimate the phonon thermal conductivity of the crystal at a temperature T = 30 K, if the concentration of impurities in it is n = 1021 m-3, and the speed of sound is s = 3•103 m/s. At what thickness of the crystal will scattering of phonons at the boundaries begin to take effect?

Detailed solution. Format gif