Choi Heechae, Song Jin Dong, Lee Kwang-Ryeol, Kim Seungchul
†Center for Computational Science and ‡Center for Optoelectronics Convergence System, Korea Institute of Science and Technology, Hwarangro 14 Gil 5, 136-791, Seoul, Korea.
Inorg Chem. 2015 Apr 20;54(8):3759-65. doi: 10.1021/ic502905m. Epub 2015 Mar 27.
The visible-light absorption and luminescence of wide band gap (3.25 eV) strontium titanate (SrTiO3) are well-known, in many cases, to originate from the existence of natural oxygen deficiency in the material. In this study based on density functional theory (DFT) calculations, we provide, to the best of our knowledge, the first report indicating that oxygen vacancies in the bulk and on the surfaces of SrTiO3 (STO) play different roles in the optical and magnetic properties. We found that the doubly charged state of oxygen vacancy (VO(2+)) is dominant in bulk SrTiO3 and does not contribute to the sub-band gap photoexcitation or intrinsic magnetism of STO. Neutral oxygen vacancies (VO(0)) on (001) surfaces terminated with both TiO2 and SrO layers induce magnetic moments, which are dependent on the charged state of VO. The calculated absorption spectra for the (001) surfaces exhibit mid-infrared absorption (<0.5 eV) and sub-band gap absorption (2.5-3.1 eV) due to oxygen vacancies. In particular, VO(0) on the TiO2-terminated surface has a relatively low formation energy and magnetic moments, which can explain the recently observed spin-dependent photon absorptions of STO in a magnetic circular dichroism measurement [Rice, W. D.; et al. Nat. Mater.13, 481, 2014].
众所周知，宽带隙（3.25电子伏特）钛酸锶（SrTiO₃）的可见光吸收和发光在许多情况下源于材料中天然氧缺陷的存在。在这项基于密度泛函理论（DFT）计算的研究中，据我们所知，我们首次报告表明，SrTiO₃（STO）体相和表面的氧空位在光学和磁性能中发挥着不同作用。我们发现，氧空位的双电荷态（VO(2+)）在体相SrTiO₃中占主导地位，对STO的子带隙光激发或本征磁性没有贡献。由TiO₂和SrO层终止的（001）表面上的中性氧空位（VO(0)）会诱导磁矩，该磁矩取决于VO的电荷态。由于氧空位，（001）表面的计算吸收光谱显示出中红外吸收（<0.5电子伏特）和子带隙吸收（2.5 - 3.1电子伏特）。特别是，TiO₂终止表面上的VO(0)具有相对较低的形成能和磁矩，这可以解释最近在磁圆二色性测量中观察到的STO的自旋相关光子吸收[赖斯，W. D.；等人，《自然·材料》13，481，2014]。
