Dislocations: a magic wand to tune thermal conductivity
Thermal conductivity is a fundamental property critical to thermoelectrics, power electronics, optoelectronics, and electric-vehicle batteries. Dislocations, as line defects, have long been recognized as phonon scattering centers that reduce lattice thermal conductivity, and dislocation engineering has achieved ultralow thermal conductivities in thermoelectric materials. However, the precise mechanisms of dislocation-phonon interactions remain experimentally unresolved due to challenges in controlling dislocation density and orientation. Recent work by Yao et al. synthesized Eshelby-twisted van der Waals GeS nanowires containing a single screw dislocation, providing a platform to study screw dislocation-phonon interactions. The shear strain induces a transformation from orthorhombic (AB-stacked) to monoclinic-like structure, with double layers shifting by ~1/4 lattice vector along the b-axis. Comparing twisted and non-twisted NWs (~200 nm diameter), a significant reduction in thermal conductivity is observed in twisted NWs. Computational analysis attributes this to shorter phonon lifetimes in the monoclinic structure, driven by shear-strain-induced metastable phase. This work demonstrates the potential of dislocation engineering for tuning thermal conductivity, though challenges in scalability and precise control remain.