Local environment and oxidation state of Mn impurity in SrTiO3 determined from XAFS data

An Improved Laboratory-Based XAFS and XES Spectrometer for Analytical Applications in Materials Chemistry Research

X-ray absorption fine structure (XAFS) and x-ray emission spectroscopy (XES) are advanced x-ray spectroscopies that impact a wide range of disciplines. However, unlike the majority of other spectroscopic methods, XAFS and XES are accompanied by an unusual access model, wherein; the dominant use of the technique is for premier research studies at world-class facilities, i.e., synchrotron x-ray light sources. In this paper we report the design and performance of an improved spectrometer XAFS and XES based on the general conceptual design of Seidler, et al., Rev. Sci. Instrum. 2014. New developme…

On the nature of change in Ni oxidation state in BaTiO3-SrTiO3 system

XAFS studies of Ni-doped Ba$_{1-x}$Sr$_x$TiO$_3$ solid solution reveal that the Ni oxidation state changes from 4 in SrTiO$_3$ to 2.5 in BaTiO$_3$ when varying $x$. This change is accompanied by a noticeable change in the interatomic Ni-O distances in the first shell. The first-principles calculations show that nickel creates an impurity band in the forbidden band gap of BaTiO$_3$ and SrTiO$_3$, which explains the appearance of intense absorption of Ni-doped samples in the visible region. The analysis of the electronic structure of doped crystals and calculations of the oxygen vacancy formatio…

Structural position and oxidation state of nickel in SrTiO3

The properties of Ni-doped strontium titanate are studied using X-ray diffraction and XAFS spectroscopy. It is shown that regardless of the preparation conditions, the SrTi1-xNixO3 solid solution and the NiTiO3 phase are the most stable phases which can coexist. According to the EXAFS data, in the single-phase sample of SrTi0.97Ni0.03O3, the Ni atoms substitute for the Ti ones and are on-center. The distortion of the oxygen octahedra is not observed. The XANES spectra analysis shows that the oxidation state of nickel in NiTiO3 is 2+, and in the SrTi1-xNixO3 solid solution it is close to 4+. It…

Si（100）表面氧化过程中的应力发展与杂质偏聚

Stress Development and Impurity Segregation during Oxidation of the Si(100) Surface

采用基于密度泛函理论的静态和动态第一性原理相结合的方法研究了Si（100）表面氧化过程中P和B杂质的偏聚.在裸露的表面中，掺杂剂分离到化学稳定的表面位点或局部压缩的亚表面位点。表面氧化是伴随着发展的拉伸表面应力高达2.9 N/m，在1.5单层的氧的覆盖率和通过形成氧化的硅物种的电荷增加近似线性与相邻的氧原子的数量。替代P和B缺陷在天然氧化物层内能量不稳定，并且优先位于Si/SiOx界面处或下方。一致地，第一性原理分子动力学模拟的掺杂表面上的原生氧化物形成揭示，掺杂剂避免P-O和B-O键的形成，这表明表面氧化机制，杂质仍然被困在Si/SiOx界面。这似乎排除了杂质对表面静电的直接影响，因此也排除了杂质对与外部环境相互作用的影响。

On the possibility of incorporation of the iron impurity into $A$ sites in SrTiO$_3$

The local environment and oxidation state of the Fe impurity in strontium titanate are studied using XAFS spectroscopy. The influence of annealing temperature and deviation from stoichiometry on the possibility of incorporation of the impurity into the $A$ and $B$ sites of the perovskite structure is studied. The results obtained from the X-ray diffraction, XANES spectra, and EXAFS spectra suggest that at high annealing temperature the iron atoms, at least partially (up to 30%), enter the $A$ sites in SrTiO$_3$. The obtained results agree with results of first-principles calculations, accordin…

Cobalt in strontium titanate as a new off-center magnetic impurity

The local structure and oxidation state of the cobalt impurity in SrTiO$_3$ is studied by X-ray absorption fine structure (XAFS) spectroscopy. The synthesis conditions, under which cobalt predominantly (up to 76%) substitutes the atoms at the $A$ site of the perovskite structure, is found for SrTiO$_3$(Co) samples. By varying the synthesis conditions, it is possible to appreciably change the ratio between the concentrations of cobalt atoms incorporated into the $A$ and $B$ sites. It is established that the oxidation state of cobalt is +2 at the $A$ site and +3 at the $B$ site. It is revealed t…