Yutong Chen, Xiangyu Zeng, Ying Wang, Wenjun Sun, A M Chen, Mingxing Jin
Abstract Two-dimensional (2D) ferroelastic materials provide a promising platform for directionally tunable thermoelectric transport because ferroelastic domain reorientation can interchange the principal crystallographic axes and thereby modulate anisotropic heat and charge transport. In this work, we systematically investigate the structural, ferroelastic, phononic, electronic, and thermoelectric properties of monolayer In 2 I 2 Te 2 using first-principles calculations combined with Boltzmann transport theory. The optimized monolayer adopts an orthorhombic structure with pronounced in-plane anisotropy and exhibits ferroelastic bistability, with a switching barrier of approximately 0.12 eV per atom. Phonon calculations confirm its dynamical stability and reveal intrinsically low and anisotropic lattice thermal conductivity, with values of 1.6 and 0.8 Wm −1 K −1 along the x and y directions at 300 K, respectively. Mode-resolved phonon analysis indicates that this low thermal conductivity originates from soft phonon branches, low-frequency acoustic–optical coupling, large Grüneisen parameters, and direction-dependent acoustic phonon group velocities and lifetimes. Electronic transport calculations show that n-type doping is more favorable than p-type doping, mainly because electrons possess lighter effective masses, longer relaxation times, and higher electrical conductivity, particularly along the x direction. As a result, monolayer In 2 I 2 Te 2 exhibits strongly anisotropic thermoelectric performance, with maximum n-type ZT values of 3.8 and 1.0 along the x and y directions at 300 K, increasing to 8.0 and 2.7 at 700 K, respectively. These results indicate that monolayer In 2 I 2 Te 2 may serve as a useful model system for exploring ferroelasticity-controlled anisotropic thermoelectric transport in 2D halogen–chalcogen compounds.