Influence of oxygen vacancy on electric structure and optical properties of pure and N-doped Sr₂M₂O₇(M = Nb, Ta)

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• 作者：Yu-Min Song ; Jian-Qing Dai ; ^{djqkust@sina.com} ; Hu Zhang
• 关键词：Sr2M2O7 ; Electronic structure ; Oxygen vacancy ; N-doped ; Optical property
• 刊名：Computational Materials Science
• 出版年：2017
• 出版时间：1 February 2017
• 年：2017
• 卷：127
• 期：Complete
• 页码：180-186
• 全文大小：1490 K
• 卷排序：127

文摘

We have investigated the electronic structure and optical properties of the pure and N-doped Sr2M2O7(M = Nb, Ta) systems with the oxygen vacancy by the HSE06 functional. For the undoped compounds, we find that the oxygen vacancy induces magnetism in both Sr2Nb2O6.75 and Sr2Ta2O6.75, in which the magnetic moments are 0.76 μB and 0.34 μB on the Nb and Ta atoms, respectively. Furthermore, the oxygen vacancy gives rise to defect electronic states near the bottom of the conduction band, which shifts the absorption border into the visible light area. For the N-doped systems, we obtain magnetic moments of 0.53 μB and 0.52 μB on the N atom for Sr2Nb2O6.75N0.25 and Sr2Ta2O6.75N0.25 respectively. Nitrogen doping induces impurity N 2p states in the band gap and thus produces visible light absorption behavior. With the introduction of the oxygen vacancy in Sr2Nb2O6.75N0.25 and Sr2Ta2O6.75N0.25, the magnetism is weakened and the impurity N 2p electronic states in the band gap disappear. There exist defect Nb 4d and Ta 5d states that lie just below the Fermi level near the conduction band for Sr2Nb2O6.5N0.25 and Sr2Ta2O6.5N0.25 respectively. This makes the absorption edge further red-shifted.