Thermal Conductivity and Lattice Vibrational Modes

This chapter discusses thermal conductivity and lattice vibrational modes. The heat transport by lattice waves in solids is governed by the anharmonicities of the lattice forces (which are also responsible for thermal expansion), by the various imperfections of the crystal lattice, and by the external boundaries. In the case of metallic and semi-metallic solids, the lattice component of thermal conduction is also governed by the free electrons. Not only may many different factors influence the thermal conductivity, but the processes that provide the principal sources of thermal resistance may vary from one material to another. In fact, they may vary in different temperature regions in any one material. Thus, the phenomenon of thermal conduction by lattice waves offers great diversity and provides an interesting field of study, both from a fundamental point of view, in which one desires to attain agreement between observation and the theoretical concepts, and from the more applied viewpoint in which one desires to use thermal conductivity as a tool in the study of lattice imperfections. Thermal conduction by lattice waves also occurs in metallic solids, but here the lattice conductivity is small, as a consequence of the scattering of lattice waves by conduction electrons, so that it is often overshadowed by the electronic thermal conductivity.