High thermal conductivity in superhard carbon nitrides: Phonon transport and thermo-mechanical Co-design

Carbon nitrides (CN) are promising structural materials for extreme environments due to their diamond-comparable bulk modulus, high wear resistance, and low friction coefficients. While research has primarily focused on the mechanical properties of CN polymorphs, their potential for thermal management remains largely unexplored. Here, comprehensive first-principles calculations reveal that three-dimensional (3D) CN polymorphs exhibit remarkable dual functionality: they possess superhard character (up to ∼60 GPa), with bulk moduli approaching or surpassing diamond (up to 433 GPa), and exceptional thermal conductivity (up to 511 W/mK at room temperature). By correlating structural features with phonon transport behavior such as phonon group velocity and scattering rates, we demonstrate how distinct crystal architectures of the same chemical composition give rise to substantial variations in thermal conductivity. Furthermore, we introduce a co-design framework integrating thermal transport and mechanical properties with micro/nanostructures, highlighting CN structures as superhard yet highly thermal conductive materials and providing guidance for the targeted selection and development of materials for advanced thermal management applications.