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981.
The compounds Rb3Sb2Br9, Rb3Sb2I9, Rb3Bi2Br9, Rb3Bi2I9, and Tl3Bi2Br9 were synthesized and their crystal structures determined from single crystal X‐ray diffraction data. The compounds Rb3Sb2Br9, Rb3Sb2I9, and Rb3Bi2I9 crystallize in the Tl3Bi2I9 type of structure (space group P21/n, no. 14). Rb3Bi2Br9 and Tl3Bi2Br9 crystallize in a new but closely related type of structure (space group P21/a, no. 14). Both structure types feature characteristic double layers comprising corner‐sharing EX6 octahedra. The space groups are set in a way that the stacking direction of the layers is the [001] direction. The group‐subgroup relations to cubic perovskite ABO3 are discussed. Differences between M3E2X9 types are attributed to distortions of the underlying MX3 close packing. Depending on the atomic size ratio, the distortions are quantified by an order parameter. 相似文献
982.
A Genuine Jahn–Teller System with Compressed Geometry and Quantum Effects Originating from Zero‐Point Motion
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Prof. José Antonio Aramburu Dr. Pablo García‐Fernández Dr. Juan María García‐Lastra Prof. Miguel Moreno 《Chemphyschem》2016,17(14):2146-2156
First‐principle calculations together with analysis of the experimental data found for 3d9 and 3d7 ions in cubic oxides proved that the center found in irradiated CaO:Ni2+ corresponds to Ni+ under a static Jahn–Teller effect displaying a compressed equilibrium geometry. It was also shown that the anomalous positive g∥ shift (g∥?g0=0.065) measured at T=20 K obeys the superposition of the |3 z2?r2? and |x2?y2? states driven by quantum effects associated with the zero‐point motion, a mechanism first put forward by O'Brien for static Jahn–Teller systems and later extended by Ham to the dynamic Jahn–Teller case. To our knowledge, this is the first genuine Jahn–Teller system (i.e. in which exact degeneracy exists at the high‐symmetry configuration) exhibiting a compressed equilibrium geometry for which large quantum effects allow experimental observation of the effect predicted by O'Brien. Analysis of the calculated energy barriers for different Jahn–Teller systems allowed us to explain the origin of the compressed geometry observed for CaO:Ni+. 相似文献
983.
984.
本文引入了由广义Dziok-Srivastava算子定义的多叶调和函数新子类, 给出了该类中函数的系数不等式, 偏差估计和极值点等性质. 相似文献
985.
Fringe projection profilometry (FPP) is a powerful method for three-dimensional (3D) shape measurement. However, the measurement accuracy of the existing FPP is often hindered by the distortion of the lens used in FPP. In this paper, a simple and efficient method is presented to overcome this problem. First, the FPP system is calibrated as a stereovision system. Then, the camera lens distortion is eliminated by correcting the captured images. For the projector lens distortion, distorted fringe patterns are generated according to the lens distortion model. With these distorted fringe patterns, the projector can project undistorted fringe patterns, which means that the projector lens distortion is eliminated. Experimental results show that the proposed method can successfully eliminate the lens distortions of FPP and therefore improves its measurement accuracy. 相似文献
986.
李菊芬 《原子与分子物理学报》2016,33(6)
本文采用对角化三角场中d5组态离子的完全能量矩阵的方法,研究了Fe3+离子在ZnO:Fe3+体系的局域结构与EPR参量的关系,结果表明:在ZnO:Fe3+体系中,Fe3+取代了Zn2+离子后整个晶体显示出压缩畸变,其畸变参量ΔR=-0.119A和Δθ=0.339°被确定。 相似文献
987.
Jing Zhang Yufeng Zhao Wanting Zhao Jing Wang Yongfeng Hu Chengyu Huang Xingli Zou Yang Liu Dengsong Zhang Xionggang Lu Hongjin Fan Yanglong Hou 《Angewandte Chemie (International ed. in English)》2023,62(52):e202314303
Transition metal single atom electrocatalysts (SACs) with metal-nitrogen-carbon (M−N−C) configuration show great potential in oxygen evolution reaction (OER), whereby the spin-dependent electrons must be allowed to transfer along reactants (OH−/H2O, singlet spin state) and products (O2, triplet spin state). Therefore, it is imperative to modulate the spin configuration in M−N−C to enhance the spin-sensitive OER energetics, which however remains a significant challenge. Herein, we report a local field distortion induced intermediate to low spin transition by introducing a main-group element (Mg) into the Fe−N−C architecture, and decode the underlying origin of the enhanced OER activity. We unveil that, the large ionic radii mismatch between Mg2+ and Fe2+ can cause a FeN4 in-plane square local field deformation, which triggers a favorable spin transition of Fe2+ from intermediate (dxy2dxz2dyz1dz21, 2.96 μB) to low spin (dxy2dxz2dyz2, 0.95 μB), and consequently regulate the thermodyna-mics of the elementary step with desired Gibbs free energies. The as-obtained Mg/Fe dual-site catalyst demonstrates a superior OER activity with an overpotential of 224 mV at 10 mA cm−2 and an electrolysis voltage of only 1.542 V at 10 mA cm−2 in the overall water splitting, which outperforms those of the state-of-the-art transition metal SACs. 相似文献
988.
989.
Persson I Eriksson L Lindqvist-Reis P Persson P Sandström M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(22):6687-6696
The structure of the solvated mercury(II) ion in water and dimethyl sulfoxide has been studied by means of large-angle X-ray scattering (LAXS) and extended X-ray absorption fine structure (EXAFS) techniques. The distribution of the Hg-O distances is unusually wide and asymmetric in both solvents. In aqueous solution, hexahydrated [Hg(OH(2))(6)](2+) ions in a distorted octahedral configuration, with the centroid of the Hg-O distance at 2.38(1) A, are surrounded by a diffuse second hydration sphere with HgO(II) distances of 4.20(2) A. In dimethyl sulfoxide, the six Hg-O and HgS distances of the hexasolvated [Hg{OS(CH(3))(2)}(6)](2+) complex are centered around 2.38(1) and 3.45(2) A, respectively. The crystal structure of hexakis(pyridine 1-oxide)mercury(II) perchlorate has been redetermined. The space group R(-)3 implies six equal Hg-O distances of 2.3416(7) A for the [Hg(ONC(5)H(5))(6)](2+) complex at 100 K. However, EXAFS studies of this compound, and of the solids hexaaquamercury(II) perchlorate and hexakis(dimethyl sulfoxide)mercury(II) trifluoromethanesulfonate, also with six equidistant Hg-O bonds according to crystallographic results, reveal in all cases strongly asymmetric Hg-O distance distributions. Vibronic coupling of valence states in a so-called pseudo-Jahn-Teller effect probably induces the distorted configurations. 相似文献
990.
用基于第一性原理的密度泛函理论研究了W(100) c(2×2)再构表面的表面弛豫以及扫描隧道显微镜(STM)图像和衬底偏压的关系. 计算所得到的表面原子沿[-110]方向的畸变位移δ为0.027 nm, 畸变能⊿E为80.6 meV·atom-1, 表面原子的弛豫分别为-7.6%(⊿d12/d0)和+0.8%(⊿d23/d0), 功函数Φ为4.55 eV. STM图像模拟表明, 由于表面原子沿[-110]方向的位移, 会导致出现平行于[110]方向的亮暗带状条纹. STM图像中突起所对应的并不是表面或次表面的钨原子, 而是zig-zag型W 原子链中线位置; 而STM暗区对应于原子位置畸变形成的相邻zig-zag型W原子链中间区域. 当衬底负偏压时, STM针尖典型起伏高度大约在0.008-0.013 nm之间; 而当衬底正偏压时, 针尖起伏高度在0.019-0.024 nm之间变化. 相似文献