
Accession Number : AD0642498
Title : HEAT FLOW IN CRYSTAL LATTICES.
Descriptive Note : Technical rept.,
Corporate Author : MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF ELECTRICAL ENGINEERING
Personal Author(s) : Magid,Leonard M.
Report Date : 12 MAY 1962
Pagination or Media Count : 154
Abstract : A direct approach to the study of the lattice component of thermal conductivity in the classical temperature range is presented in terms of the mechanical energy transported. Both a mechanical 'Poynting' vector and an Energy Flow Theorem, linking the power flow to the group velocity, are derived. Furthermore, these concepts are extended to include the manner in which both lattice imperfections and temperature gradients lead to a statistical steadystate energy distribution. In this phase of the work, statistical ensembles of normal modes with space and timedependent amplitudes are used in a classical secondorder perturbation scheme to solve for the steadystate dynamics of the nonlinear lattice system. A linear energy (i.e. temperature) gradient, an unambiguous calculation of the accepted lattice relaxation times, and finally the evaluation directly from the mechanical power densities of the wellknown anharmonic, massfluctuation, and forcefluctuation components of thermal conductivity are some of the more significant firstorder results. All this work is based upon a completely general, 3dimensional crystal. No need is found for restrictive assumptions as to lattice symmetry, number of atoms per unit cell, or nearness of interacting neighbors. Electronic contributions to heat flow, and size effects, however, have been omitted. No use is made of the Boltzmann Transport Equation, although the results are found to be wholly consistant with it. (Author)
Descriptors : (*CRYSTAL LATTICES, *THERMAL CONDUCTIVITY), THEOREMS, TRANSPORT PROPERTIES, STATISTICAL DISTRIBUTIONS
Subject Categories : Crystallography
Thermodynamics
Distribution Statement : APPROVED FOR PUBLIC RELEASE