Electron and phonon transport properties of layered Bi₂O₂Se and Bi₂O₂Te 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.

T-square resistivity without Umklapp scattering in dilute metallic Bi2O2Se

“…Our DFT calculations of phonon spectrum for the tetragonal phase of Bi 2 O 2 Se are in agreement with what was reported previously 27,28 . Figure 1c presents the phonon dispersion at ambient pressure.…”

Band degeneracy enhanced thermoelectric performance in layered oxyselenides by first-principles calculations

“…two crystals exhibit strong anisotropy. Similar phenomena have been observed in other layered materials 10,43 .…”

“…More important is that the highest PF value of n-type LaCuOSe is 2.58 mW m −1 K −2 at 300 K, which is 1.5 times larger than that of 1.71 mW m −1 K −2 for n-type BiCuOSe. This value is also found larger than the optimal PF values of many layered TE materials at room temperature, such as Bi 2 O 2 Se (~0.4 mW m −1 K −2 ) 43 and Bi 2 O 2 Te (~0.55 mW m −1 K −2 ) 43 . Higher power factor of n-type LaCuOSe is mainly because the larger Seebeck coefficient caused by conduction band degeneracy and higher optimal carrier concentration (which corresponds to a higher electrical conductivity).…”

Surface electronic structure of bismuth oxychalcogenides

“…The direct ( -) gap values, 1.307 eV (mBJ) and 1.340 eV (HSE06), are in reasonable agreement with the optical absorption band gap. Earlier calculations performed within the mBJ approach [51,53,75,76] demonstrated the gap varying from 0.85 eV [53] to 1.28 eV [51]. The larger value was obtained when the van der Waals (vdW) corrections were not taken into account during the structure optimization and hence the lattice parameters (especially c) were overestimated.…”