Minimum thermal conductivity in the context of diffuson-mediated thermal transport
A model for the thermal conductivity of bulk solids is proposed in the limit of diffusive transport mediated by diffusons as opposed to phonons. This diffusive thermal conductivity, κdiff, is determined by the average energy of the vibrational density of states, ℏωavg, and the number density of atoms, n. Furthermore, κdiff is suggested as an appropriate estimate of the minimum thermal conductivity for complex materials, such that (at high temperatures): . A heuristic finding of this study is that the experimental ωavg is highly correlated with the Debye temperature, allowing κdiff to be estimated from the longitudinal and transverse speeds of sound: . Using this equation to estimate κmin gives values 37% lower than the widely-used Cahill result and 18% lower than the Clarke model for κmin, on average. This model of diffuson-mediated thermal conductivity may thus help explain experimental results of ultralow thermal conductivity.
- This article is part of the themed collection: 2018 Energy and Environmental Science HOT Articles