The Role of Phonon Anharmonicity on the Structural Stability and Phonon Heat Transport of Crfeconicux High-Entropy Alloys at Finite Temperatures

Chemical disorder and lattice distortion make high-entropy alloys (HEAs) promising to become a new generation of thermoelectric materials. However, the large parameter space of HEAs makes it still a great challenge to study their anharmonic unfolded phonon properties, and the role of anharmonicity in their structural stability and phonon heat transport is still unclear. Here we provide a new scheme to achieve a breakthrough in obtaining the unfolded anharmonic phonon properties from the dynamic trajectories. Through careful analysis of the unfolded phonon dispersions, we found that CrFeCoNiCu HEA has a special anharmonic phonon scattering distribution, which makes the contribution of short-wavelength and long-wavelength phonons to lattice thermal conductivity significantly different. In addition, we have developed a model for estimating the formation energy of HEAs based on the formation energy of binary alloy from first-principles calculation. Our results also show that anharmonic phonon scattering plays an important role in the stability of CrFeCoNiCu x HEAs solid-solution phase, which also complements the dynamic mechanism of the formation and stability of dual-FCC phase. CrFeCoNiCu HEA has very low lattice thermal conductivity even at extremely low temperatures. The contribution of long-wavelength phonons to lattice thermal conductivity is more than ten times that of short-wavelength phonons, and they are the main contributors of phonon heat transport of CrFeCoNiCu HEA. This study makes it possible to study the unfolded phonon properties of HEAs at finite temperature, and provides important theoretical support and information for the stability of solid-solution structure and phonon engineering for HEAs.