Systematically investigate mechanical and electrical properties of Bi2O2Se by Te atom substitution and compare it with homologue Bi2O2Te from first-principles calculations

In this paper, first-principles calculations based on density functional theory (DFT) were used to study the optimization of the mechanical and electrical properties of Bi2O2Se by equivalent Te atom substitution (Bi2O2Se1-XTeX (X = 0, 0.25, 0.50, 0.75, 1)). The structures of Te atom after equivalent substitution satisfy the mechanical stability, and can improve its plastic toughness. The minimum thermal conductivity (k(min)) of Bi2O2Se1-XTeX (X = 0, 0.25, 0.50, 0.75, 1) determined by elastic constants are 0.398 (W/m k), 0.362 (W/m k), 0.332 (W/m k), 0.376 (W/m k), 0.36 (W/m k) and Debye-temperature (T-D) are 287.0 K, 263.4 K, 245.9 K, 274.6 K, 266.7 K, respectively. The values indicate that the substitution of Te atoms can inhibit the heat transfer and reduce the atomic bonding force to improve the toughness. And the effect is best when the concentration of Te atom substitution reaches 0.5. The calculated energy band gaps (E-g) of Bi2O2Se1-XTeX (X = 0, 0.25, 0.50, 0.75, 1) are 0.85 eV, 0.52 eV, 0.18 eV, 0.11 eV and 0.23 eV, respectively. The E-g of Bi2O2Se and Bi2O2Te are consistent with the experimental results. Electronic structure analysis shows that Te atom substitution makes s-orbital and p-orbit hybridization stronger and Fermi level (E-F) right shift, and then narrows the band gap. It is more directly reflected in the charge density difference and electron localization function (ELF) maps. The results show that the substitution of Te atom for Se atom in the Bi2O2Se can improve the mechanical and electrical properties, and then improve the actual conversion efficiency of thermoelectricity.