The Effective Regulation of Anisotropic Thermal Properties in Three‐Dimensional ZnSe Through Cu Substitution

In our study of the thermal transport properties of ZnSe during the substitution process, we surprisingly found that the proportion of Cu substitution can effectively regulate the anisotropy of ZnSe’s thermal conductivity (TC). Specifically, 50% Cu substitution induces a pronounced anisotropy, while the other substitution levels (0%, 25%, and 75%) exhibit isotropic TC. In this structure, the contribution of optical phonons to TC anomalously exceeds that of the acoustic phonon branches. This phenomenon fundamentally arises because optical phonons possess relatively high group velocities, enabling them to cross the LA branch and strongly interact with the TA branches. More importantly, such interactions also cause hybridization at the crossing points, leading to the opening of bandgaps, while also splitting two degenerate TA branches into distinct ones. As a result, the 50% substituted model exhibits anisotropic TC. Further analysis of bonding strength and mechanical properties shows that the 50% substituted model displays the most pronounced differences in bond strength, with its Young’s modulus, shear modulus, and Poisson’s ratio all presenting significant anisotropy. This provides both structural and mechanical explanations for the observed anisotropy in TC.