Do dislocations always decrease thermal conductivity?

Abstract

Dislocations play a significant role in introducing disorder and distortion within an ideal bulk crystal lattice, resulting in the degradation of phonon thermal conductivity. In this study, we employ non-equilibrium Molecular Dynamics (NEMD) simulations to investigate the thermal conductivity of two spherical, single-crystal face-centered cubic (fcc) nanoparticles (NP) with a radius denoted as R. Our analysis encompasses pristine interfaces as well as interfaces containing dislocations, at the NP contact. Surprisingly, our findings reveal that the presence of dislocations leads to an increase in thermal conductivity, contrary to the expectations derived from bulk models and simulations. This counterintuitive behavior can be attributed to the expansion of the contact radius (ac) between the nanoparticles, facilitated by the dislocations. Notably, the thermal conductivity demonstrates a substantial reduction of approximately 90% compared to bulk values, and in all simulated cases, it scales effectively as a function of (ac/R). We explore various models to elucidate the impact of dislocations on thermal conductivity and ascertain that, under our specific conditions, only a marginal decrease would be anticipated. In alignment with these models, our results indicate that the introduction of localized dislocation arrays spanning nearly ten lattice parameters into a bulk sample elicits a thermal conductivity decrease of less than 10%. These findings provide compelling evidence that dislocations per se do not significantly affect thermal conductivity. Instead, the enhanced contact area generated by dislocations governs the heat flux within the simulated nanostructures. Notably, the analysis of thermal boundary conductance, which evaluates the conductivity across the interfaces, does exhibit a decrease in interfaces featuring dislocations. Considering that the dislocation content can be influenced by various synthesis conditions of the nanoparticles, these findings hold promising implications for tailoring the thermal conductivity of nanoparticle beds or coatings.