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Using first-principles calculations based on density functional theory, we systematically investigated the electronic properties and charge transfer of topological insulator Bi2Te3−xSex thin films under an external electric field. As the selenium content in Bi2Te3−xSex thin films increases, the band gap is gradually opened, with changes in the charge distribution. In addition, the experimentally stable Bi2Te2Se and Bi2Se2Te thin films are extremely robust under vertical electric fields up to 0.2 V Å−1. The electronic structures of Bi2Te2Se and Bi2Se2Te thin films are insensitive to the electric fields and exhibit only a Rashba-like splitting pattern near the Fermi level. Remarkably, the charge transfer in Bi2Te2Se and Bi2Se2Te thin films under an external electric field is suppressed. We found that the robustness characteristic is inextricably linked to the strong covalent bonding of tellurium and bismuth atoms. These results indicated that Bi2Te2Se and Bi2Se2Te thin films are robust to the internal electrical field during growth on the substrate, which is beneficial for experimental studies as well as for the potential applications of spintronic devices. [ABSTRACT FROM AUTHOR]

Heteroatom doping is an effective way to modulate the local structure of TiO2-based materials, enabling enhanced electrochemical performance. However, current studies generally adopt a single atom doping strategy, and ionic group doping has rarely been achieved and is a distinctly bigger challenge. Herein, doping of the phosphate group at high concentrations into blue TiO2(B) nanowires is proposed and realized for the first time by skillfully utilizing the defects induced during the dehydration and topology transformation process of the H-titanate precursor; based on experimental characterization and first-principles calculations, it has been demonstrated that this material possesses exceptional electrical properties, a remarkably reduced band gap, magnetic characteristic from the extra electrons outside the Ti atomic nucleus and remarkable phase stability. Benefiting from the unusual structure properties, phosphate-doped TiO2(B) exhibits the ultra-fast sodium storage capability of 124 mA h g−1 at the extremely high rate of 50 A g−1 and excellent long cycling stability even at 10 A g−1 after 5000 cycles. Moreover, this electrode material was tested at low temperatures and exhibited comparable reversible capacity and outstanding cycling stability to those at normal temperatures. We also assembled a B–TiO2(B)–P//(NVPF) full cell, which delivered the maximum energy density of 170 Wh kg−1 and the maximum power density of 5000 W kg−1. [ABSTRACT FROM AUTHOR]

Using first-principles calculations based on density functional theory, we systematically investigated the electronic properties and charge transfer of topological insulator Bi 2 Te 3-x Se x thin films under an external electric field. As the selenium content in Bi 2 Te 3-x Se x thin films increases, the band gap is gradually opened, with changes in the charge distribution. In addition, the experimentally stable Bi 2 Te 2 Se and Bi 2 Se 2 Te thin films are extremely robust under vertical electric fields up to 0.2 V Å -1 . The electronic structures of Bi 2 Te 2 Se and Bi 2 Se 2 Te thin films are insensitive to the electric fields and exhibit only a Rashba-like splitting pattern near the Fermi level. Remarkably, the charge transfer in Bi 2 Te 2 Se and Bi 2 Se 2 Te thin films under an external electric field is suppressed. We found that the robustness characteristic is inextricably linked to the strong covalent bonding of tellurium and bismuth atoms. These results indicated that Bi 2 Te 2 Se and Bi 2 Se 2 Te thin films are robust to the internal electrical field during growth on the substrate, which is beneficial for experimental studies as well as for the potential applications of spintronic devices.

Magnetic doping in topological insulator Sb 2 Te 3 can produce very novel physical phenomena such as quantum anomalous Hall effect (QAHE). However, experimental observations of QAHE in the magnetic atoms doped Sb 2 Te 3 have encountered significant challenges due to the complexity of the electronic structure and the relatively small band gap. Generally, mechanical strain can effectively modulate the band structure, thus we theoretically investigate the electronic structures of Cr-doped Sb 2 Te 3 under mechanical strain using first-principles calculations within density functional theory. The band gap of Cr-doped Sb 2 Te 3 is 0.031 eV. When the compressive strain η becomes as  -2%, the band gap will be further enlarged to 0.045 eV, which is 45% larger than that of the unstrained material. However, as the compressive strain η exceed  -2%, strong hybridization between Cr and Te atoms will cause the overlap of bands, which leads to the closure of band gap. In addition, when tensile strain is applied to Cr-doped Sb 2 Te 3 , the decrease in the spacing between quintuple layers can enhance the coupling between Te and Sb atoms, which can also result in the closing of the band gap. Finally, we used HSE06 to calculated the band gaps. The band gaps may be underestimated, but HSE06 and GGA have the same band structures evolution tendency under mechanical strain. Our calculated results provide a guideline for the modulation of band structure by mechanical strain, which pave the way for the observation of QAHE in Cr-doped Sb 2 Te 3 .