Synergistically optimizing electrical and thermal transport properties of Bi 2 O 2 Se ceramics by Te‐substitution

Abstract Bi 2 O 2 Se oxyselenides, characterized with intrinsically low lattice thermal conductivity and large Seebeck coefficient, are potential n ‐type thermoelectric material in the mediate temperature range. Given the low carrier concentration of ~10 15 cm −3 at 300 K, the intrinsically low electrical conductivity actually hinders further enhancement of their thermoelectric performance. In this work, the isovalent Te‐substitution of Se plays an effective role in narrowing the band gap, which notably increases the carrier concentration to ~10 18 cm −3 at 300 K and the electron conduction activation energy has been lowered significantly from 0.33 to 0.14 eV . As a consequence, the power factor has been improved from 104 μW·K −2 ·m −1 for pristine Bi 2 O 2 Se to 297 μW·K −2 ·m −1 for Bi 2 O 2 Se 0.96 Te 0.04 at 823 K. Meanwhile, the suppressed lattice thermal conductivity derives from the introduced point defects by heavier Te atoms. The gradually decreased phonon mean free path reflects the increasingly intense phonon scattering. Ultimately, the ZT value attains 0.28 for Bi 2 O 2 Se 0.96 Te 0.04 at 823 K, an enhancement by a factor of ~2 as compared to that of pristine Bi 2 O 2 Se. This study has demonstrated that Te‐substitution of Se could synergistically optimize the electrical and thermal properties thus effectively enhancing the thermoelectric performance of Bi 2 O 2 Se.