Gradient engineering enabled thermoelectric performance optimization in LaP/LaAs heterostructures.

Within condensed matter physics and materials science, the synergistic effect of band engineering and phonon engineering can greatly enhance the thermoelectric performance of functional materials. In this study, we focus on the gradient engineering in a LaP/LaAs heterostructure and systematically investigate its structure, lattice dynamics, and thermoelectric properties through first-principles calculations. The interface modulation of the heterostructure changes the phonon dispersion curves, leading to the collective vibrational behavior of the low-frequency optical branches and their strong coupling with the acoustic branches. The strong hybridization of La-d and P/As-p orbitals changes the band dispersion relation, and the spin-orbit coupling induces orbital rearrangement at the band edges, resulting in quasi-reversed band dispersion characteristics, which optimizes the carrier transport channel and improves the mobility and conductivity of the carriers. These combined effects lead to a significant improvement in the thermoelectric figure of merit, ZT, in the optimized LaP/LaAs heterostructure; the value reaches a maximum of 0.69 along the a-axis at 900 K and 0.56 along the c-axis. This study demonstrates the application potential of gradient engineering in the LaP/LaAs heterostructure, which overcomes the inherent limitations of traditional thermoelectric materials and provides a novel approach for optimizing thermoelectric performance.