General theory for designing phonon transport in alloyed/doped materials

Alloying/doping is a widely used technique for improving the electrical, mechanical, and optical properties of materials. However, this technology induces significant distortions in the lattice structure, mass distribution, and potential field, greatly enhancing phonon scattering. Here, we introduce the concept of alloying/doping path and employ crystal symmetry, lattice deformation, and electron distribution to characterize it. Based on this new concept, the phonon thermal transport behavior in alloyed/doped materials can be well designed, and along different alloying/doping paths, the difference in thermal conductivity can be up to 45 times. On one hand, strategic alloying/doping that combines high crystal symmetry, large lattice contraction, and the same electron distribution suppresses phonon-phonon scattering phase space, induces phonon stiffening, and bolsters electronic structure symmetry, respectively. These synergistic effects significantly improve thermal conductivity. On the other hand, random alloying/doping has a low symmetry, leading to the typical “U” shape of alloying/doping level-dependent thermal conductivity. Our theory is corroborated in three-dimensional (3D) Si, 2D MoS₂, and quasi-1D TiS₃, affirming its efficacy and broad applicability in controlling phonon transport.