ABSTRACT
This chapter presents the experimental techniques currently used for measuring phonon velocities and lifetimes: inelastic neutron and X-rays scattering. A crystal contains an extremely large number (N) of atoms, of the order of the Avogadro number, chemically bounded and arranged in an ordered microscopic structure. The difficulty in studying the dynamics of amorphous materials stems from the absence of any possible simplification in the structural description of the system. The lack of long- range periodicity hinders the application of the theories developed for lattice dynamics in crystals; moreover the disordered structure is not close enough to a simpler ordered one, to allow for a perturbative approach to be used for solving the dynamics of the system. Thermal properties of materials, amorphous, crystalline, or com- posites, are at the focus of the modern research, for a variety of applications.
