Fig. 6: The dispersion relation for a phonon in the case of diatomic materials in 3D form.

a The predominant routes of phonon decay start from their origin center as LO phonons and progressively turn into lower energy acoustic phonons that are responsible for the dissipation of heat. b The four types of decay mechanisms are depicted as Klemens, Ridely, Vallee–Bogani, and Barman–Sirvastava. The figures are taken with permission from ref. 13