Thermal Transport in Disordered Materials

We review the status of research on thermal/phonon transport in disordered materials. The term disordered materials is used here to encompass both structural and compositional disorder. It includes structural deviations ranging from an ideal crystal with disordered arrangements of defects all the way to fully amorphous materials, as well as crystals with impurities up through multi-component random alloys. Both types of disorder affect phonons by breaking the symmetry of an idealized crystal and changing their character/mode shapes. These effects have important implications with regard to phonon-phonon interactions, phonon transport and phonon interactions with other quantum particles, which are being actively investigated. Herein, we synthesize the current theoretical understanding, identify the aspects of the problem that require more work, and pose open questions. Abbreviations: BTE: Boltzmann transport equation; DFT: Density functional theory; EPP: Eigenvector periodicity parameter; FAFDTR: Fiber-aligned frequency domain thermoreflectance; GK: Green-Kubo; GKMA: Green-Kubo modal analysis; HCACF: Heat current autocorrelation function; IXS: Inelastic X-ray scattering; LD: Lattice dynamics; LJ: Lennard-Jones; MD: Molecular dynamics; MFP: Mean free path; NEMD: Non-equilibrium molecular dynamics; NMD: Normal-mode dynamics; PDL: Propagon, diffuson, locon; PGM: Phonon gas model; PR: Participation ratio; SCLD: Supercell lattice dynamics; SED: Spectral energy density; TDTR: Time-domain thermoreflectance; VCA: Virtual crystal approximation;