Ultrahigh thermal conductivity of carbon allotropes with correlations with the scaled Pugh ratio

Abstract

Electrical insulators with ultrahigh thermal conductivity (κ_L) are highly desirable for thermal management to facilitate heat extraction in many electronic devices. In this work, we select three typical carbon allotropes (lonsdaleite, Bct-C4, and Z-carbon) with ultrahigh κ_L from the 522 carbon allotropes in the Samara Database by using Boltzmann transport theory combined with first-principles calculations. We find that the thermal conductivity (κ_L) of the three carbon allotropes is 1686.67, 1411.02 and 1262.05 W m⁻¹ K⁻¹, respectively, at room temperature. A further analysis of both harmonic and anharmonic properties reveals that such high κ_L is attributed to their exceptional atomic structures. They all are composed of pure sp³ hybridized carbon with a short bond length, small unit cell and strong chemical bonding. Together with diamond, they are the top four κ_L materials (beyond 1000 W m⁻¹ K⁻¹) reported so far among the 3D carbon allotropes. Equally important, we propose a simple descriptor, namely the scaled Pugh ratio (G/K/n), to characterize the strength of chemical bonding for high-throughput thermal material screening. The three identified carbon allotropes in this study would be alternatives to diamond in future thermal energy devices.