The Electronic Structures and Optical Properties of Alkaline-Earth Metals Doped Anatase TiO2: A Comparative Study of Screened Hybrid Functional and Generalized Gradient Approximation
Abstract
:1. Introduction
2. Results and Discussion
2.1. Local Structures
Quantity | Ti | Be | Mg | Ca | Sr | Ba |
---|---|---|---|---|---|---|
AEM-O1 | 2.004 | 2.043 | 2.177 | 2.249 | 2.383 | 2.483 |
AEM-O2 | 2.004 | 2.042 | 2.178 | 2.248 | 2.383 | 2.483 |
AEM-O3 | 1.946 | 1.888 | 2.028 | 2.274 | 2.327 | 2.435 |
AEM-O4 | 1.946 | 1.888 | 2.028 | 2.276 | 2.328 | 2.434 |
AEM-O5 | 1.946 | 1.888 | 2.028 | 2.274 | 2.327 | 2.435 |
AEM-O6 | 1.946 | 1.888 | 2.028 | 2.276 | 2.328 | 2.434 |
Δ | 0 | –0.025 | 0.126 | 0.301 | 0.380 | 0.485 |
Ionic-radius | 0.53 | 0.31 | 0.65 | 0.99 | 1.13 | 1.35 |
2.2. Formation Energy
Dopant Atom | GGA | HSE06 | ||
---|---|---|---|---|
O-Rich | Ti-Rich | O-Rich | Ti-Rich | |
Be | 3.50 | 8.74 | 5.89 | 11.66 |
Mg | 1.80 | 7.04 | 3.38 | 9.15 |
Ca | 2.20 | 7.44 | 1.75 | 7.52 |
Sr | 2.76 | 8.00 | 2.31 | 8.08 |
Ba | 3.68 | 8.92 | 2.74 | 8.51 |
2.3. Electronic Properties
2.3.1. PBE Results
2.3.2. HSE06 Results
2.4. Optical Properties
3. Computational Methods
Functional | PBE0 | B3LYP | HSE03 | HSE06 | Experiment |
---|---|---|---|---|---|
Band gap (eV) | 4.46 | 4.00 | 3.71 | 3.69 | 3.20 |
4. Conclusions
- Viewing from methodology, by combining the previous studies with our results, including band gaps and the dopant states, HSE06 provides a better description of the electronic structures.
- The formation energies indicate that the substitution of a lattice Ti atom with an AEM atom is more energetically favorable under O-rich growth conditions than those of Ti-rich cases.
- Based upon the HSE06 results, the analysis of electronic structures suggest that, AEM dopants shift the VBs to higher energy, and the more important is that the energies of dopant states for the cases of Ca, Sr, and Ba are quite higher than the top of VBs, while the Be and Mg dopants result into the spin polarized dopant states near Fermi levels. The components of VBs, CBs and dopant states support that the AEM dopants are active in inter-band transitions induced by lower energy excitations, which is important for the application of solar energy.
- Compared with anatase TiO2, the AEM dopants shift the absorption to longer wavelength and improve optical absorbance in visible and near-IR region. The Ca, Sr, and Ba dopants are superior to Be and Mg dopants to enhance absorbance in visible region, inversely, the Be and Mg dopants are better than Ca, Sr and Ba dopants for the improvement of absorbance in near-IR region. The compensating optical absorbance of Be/Mg and Ca/Sr/Ba dopants in different wavelength region present that the Be/Mg and Ca/Sr/Ba co-doped anatase TiO2 may possess prominent optical absorption properties.
Supplementary Materials
Acknowledgments
Author Contributions
Conflicts of Interest
References
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Ma, J.-G.; Zhang, C.-R.; Gong, J.-J.; Wu, Y.-Z.; Kou, S.-Z.; Yang, H.; Chen, Y.-H.; Liu, Z.-J.; Chen, H.-S. The Electronic Structures and Optical Properties of Alkaline-Earth Metals Doped Anatase TiO2: A Comparative Study of Screened Hybrid Functional and Generalized Gradient Approximation. Materials 2015, 8, 5508-5525. https://doi.org/10.3390/ma8085257
Ma J-G, Zhang C-R, Gong J-J, Wu Y-Z, Kou S-Z, Yang H, Chen Y-H, Liu Z-J, Chen H-S. The Electronic Structures and Optical Properties of Alkaline-Earth Metals Doped Anatase TiO2: A Comparative Study of Screened Hybrid Functional and Generalized Gradient Approximation. Materials. 2015; 8(8):5508-5525. https://doi.org/10.3390/ma8085257
Chicago/Turabian StyleMa, Jin-Gang, Cai-Rong Zhang, Ji-Jun Gong, You-Zhi Wu, Sheng-Zhong Kou, Hua Yang, Yu-Hong Chen, Zi-Jiang Liu, and Hong-Shan Chen. 2015. "The Electronic Structures and Optical Properties of Alkaline-Earth Metals Doped Anatase TiO2: A Comparative Study of Screened Hybrid Functional and Generalized Gradient Approximation" Materials 8, no. 8: 5508-5525. https://doi.org/10.3390/ma8085257