Electron and phonon transport properties of layered Bi 2 O 2 Se and Bi 2 O 2 Te from first-principles calculations

Abstract

Recent experiments indicated that both layered Bi 2 O 2 Se and Bi 2 O 2 Te are promising thermoelectric materials with low thermal conductivities. However, theoretical study on the thermoelectric properties, especially the phonon transport properties, is rare. In order to understand the thermoelectric transport mechanism, we here investigate the electron and phonon transport properties by using the first-principles calculations combined with the Boltzmann transport theory. Our results indicate that both Bi 2 O 2 Se and Bi 2 O 2 Te are semiconductors with indirect energy gaps of 0.87 eV and 0.21 eV within spin-orbit coupling, respectively. Large Seebeck coefficient and power factor are found in the p-type than the n-type for both compounds. Low lattice thermal conductivities at room temperature are obtained, 1.14 W m -1 K -1 for Bi 2 O 2 Se and 0.58 W m -1 K -1 for Bi 2 O 2 Te, which are close to the experimental values. It is found that the low-frequency optical phonon branches with higher group velocity and longer lifetime also make a main contribution to the lattice thermal conductivity. Interestingly, the lattice thermal conductivity exhibits obvious anisotropy especially for Bi 2 O 2 Te. These results are helpful for the understanding and optimization of thermoelectric performance of layered Bi 2 O 2 Se and Bi 2 O 2 Te.