Structural distortion-induced band gap and localized lattice modification enhance thermoelectric properties of InTe.

InTe has attracted attention for thermoelectric applications due to its low thermal conductivity, originating from the anharmonic bonding of In 1+ , which scatters phonons in the lattice. However, its narrow band gap of about 0.12 eV results in bipolar conductivity and a low Seebeck coefficient. Here, we investigated the effect of Sb and Bi substitutional doping at the In site, which induces structural distortions that widen the band gap, increase the Seebeck coefficient, and suppress bipolar conduction. The structural distortion is evidenced by lattice expansion, modified atomic interactions, and strain-driven band dispersion. Maximum zT values of 0.75 and 0.82 were achieved for In 0.99 Bi 0.01 Te and In 0.99 Sb 0.01 Te, respectively. Moreover, the distortion also weakens the interatomic bonding, enhances phonon anharmonicity, and consequently reduces the lattice thermal conductivity. Additional phonon scattering from Bi 2 Te 3 , Sb 2 Te 3 precipitates, and In 4 Te 3 nanostructures enables multiscale phonon scattering, leading to an ultralow lattice thermal conductivity of 0.27 W·m –1 ·K –1 at 773 K. The findings highlight that structural distortion is a compelling approach for narrow-bandgap chalcogenides, offering an effective route to simultaneously tune electronic structure and activate multiscale phonon scattering to optimize thermoelectric properties.