Reduced lattice thermal conductivity through tailoring of the crystallization behavior of NbCoSn by V addition

Nanostructuring is a key approach for reducing lattice thermal conductivity. Amorphous precursors can be used to obtain complex nanostructures, as their crystallization behavior can be controlled by varying their composition, temperature, and annealing time. Herein, we investigated the effects of V alloying on the crystallization behavior and resulting lattice thermal conductivity of amorphous NbCoSn alloys. After heat treatment at 783 K for 2 h, the V-containing alloy showed a significantly finer grain size (100 ± 30 nm) than the alloy without V (870 ± 360 nm) owing to the different crystallization kinetics. We revealed that Sn-rich nanoprecipitates with a diameter of 10 nm acted as heterogeneous nucleation sites for crystallization, resulting in a finer grain size in the V-containing alloy. As a result, the V-containing alloy exhibited a lower lattice thermal conductivity (2.6 ± 0.2 W m⁻¹ K⁻¹) than the alloy without V (3.3 ± 0.2 W m⁻¹ K⁻¹) at room temperature owing to increased phonon scattering at the grain boundary, point defects, and nanoprecipitates.