Synthesis, crystal structure, and photocatalytic activity of a new two-layer Ruddlesden-Popper phase, Li2CaTa2O7

A new two-layer Ruddlesden-Popper phase Li₂CaTa₂O₇ has been synthesized for the first time. The detailed structure determination of Li₂CaTa₂O₇ performed by powder X-ray diffraction (XRD) and electron microscopy (ED) shows that it crystallizes in the space group Fmmm [a∼5.5153(1), b∼5.4646(1), c∼18.2375(3)Å]. UV-visible diffuse reflection spectrum of the prepared Li₂CaTa₂O₇ indicates that it had absorption in the UV region. The photocatalytic activity of the Li₂CaTa₂O₇ powders was evaluated by degradation of RhB molecules in water under ultra visible light irradiation. The results showed that Li₂CaTa₂O₇ has high photocatalytic activity at room temperature. Therefore, the preparation and properties studies of Li₂CaTa₂O₇ with a two-layer Ruddlesden-Popper structure suggest potential future applications in photocatalysis.     

Preparation of LiCoO2 concaved cuboctahedra and their electrochemical behavior in lithium-ion battery

LiCoO(2) concaved cuboctahedra with a size of about 1.0 μm were hydrothermally prepared from CoCO(3) and LiOH·H(2)O at 150 °C. Field-emitting scanning electron microscope (FESEM) images show that the cuboctahedra consisted of four hexagonal plates, with angles of 70.5° in neighboring plates. Electron diffraction (ED) patterns of the hexagonal plates show 1 0 0 diffraction of LiCoO(2) in rhombohedral phase and 2?2?0 diffraction in spinel phase, which means LiCoO(2) concaved cuboctahedra are comprised of two intergrown phases. The electrochemical performance of these concaved cuboctahedra of LiCoO(2) at a rate of 0.5 C demonstrated first run charge/discharge capacities of 155 and 141 mAh g(-1) and a stable discharge capacity of 114 mAh g(-1) after 100 cycles. After that, FESEM images show the LiCoO(2) concaved cuboctahedra have undergone no significant change. At a temperature of 120 °C and under the same conditions, only a small amount of LiCoO(2) concaved cuboctahedron appeared. As the temperature rose to 180 °C, flower-like LiCoO(2) microstructures with a size of about 1.0 μm were formed, constructed of irregular plates. The electrochemical performance of the products prepared at 120 °C and 180 °C indicates lower stability than that of LiCoO(2) concaved cuboctahedra.     

Synthesis of Fe2+ Substituted High-Performance LiMn1−xFexPO4/C (x = 0, 0.1, 0.2, 0.3, 0.4) Cathode Materials for Lithium-Ion Batteries via Sol-Gel Processes

A series of carbon-coated LiMn_1−xFe_xPO₄ (x = 0, 0.1, 0.2, 0.3, 0.4) materials are successfully constructed using glucose as carbon sources via sol-gel processes. The morphology of the synthesized material particles are more regular and particle sizes are more homogeneous. The carbon-coated LiMn_0.8Fe_0.2PO₄ material obtains the discharge specific capacity of 152.5 mAh·g⁻¹ at 0.1 C rate and its discharge specific capacity reaches 95.7 mAh·g⁻¹ at 5 C rate. Iron doping offers a viable way to improve the electronic conductivity and lattice defects of materials, as well as improving transmission kinetics, thereby improving the rate performance and cycle performance of materials, which is an effective method to promote the electrical properties.     

Synthesis and characterization of a new four-layer Aurivillius phase Bi2SrNa2Nb4O15 and its protonated form

A new four-layer Aurivillius phase Bi₂SrNa₂Nb₄O₁₅ has been synthesized by solid-state reaction of Bi₂SrNb₂O₉ and NaNbO₃ at 1100 °C. The detailed structure determination of Bi₂SrNa₂Nb₄O₁₅ performed by powder X-ray diffraction (XRD) shows that it crystallizes in the space group I4/mmm [a∼3.9021(1) Å, c∼40.7554(10) Å]. Protonated form of Bi₂SrNa₂Nb₄O₁₅ was obtained by the substitution of bismuth oxide sheets with protons via acid treatment. The conversion into the protonated forms was achieved easily using 6 M HCl at room temperature. Preservation of the structure of the perovskite-like slabs and contraction in the c-axis were confirmed by X-ray analysis. The compositions of the resulting products were determined to be H_1.8[Sr_0.8Bi_0.2Na₂Nb₄O₁₃] by X-ray fluorescence spectroscopy (XFS) and thermogravimetry.     

Synthesis, crystal structure, and photocatalytic activity of the new three-layer aurivillius phases, Bi2ASrTi2TaO12 (A=Bi, La)

Two new three-layer Aurivillius phases Bi₂ASrTi₂TaO₁₂ (A=Bi, La) have been synthesized. The detailed structure determination of Bi₂ASrTi₂TaO₁₂ (A=Bi, La) performed by powder X-ray diffraction (XRD) and selected area electron microscopy (SAED) shows that they all crystallize in the space group I/4mmm. UV-visible diffuse reflection spectrum of the prepared Bi₂ASrTi₂TaO₁₂ (A=Bi, La) indicates that it had absorption in the ultraviolet (UV) region. The photocatalytic activity of the Bi₂ASrTi₂TaO₁₂ (A=Bi, La) powders was evaluated by degradation of rhodamine B (RB) molecules in water under UV light irradiation. The results showed that Bi₂ASrTi₂TaO₁₂ (A=Bi, La) has high photocatalytic activity at room temperature. Therefore, the preparation and properties studies of Bi₂ASrTi₂TaO₁₂ (A=Bi, La) with a three-layer Aurivillius structure suggest potential future applications in photocatalysis.     

KMnF3晶体的简单溶液合成及发光特性研究

利用简单的液相合成方法,在室温下制备了KMnF3圆盘状产物,盘的直径约为300nm.通过X射线粉末衍射(XRD)、透射电镜以及选区电子衍射对它的结构成分和物相进行了表征,发现圆盘形貌是由KMnF3小颗粒自组装而形成的.同时对样品的发光性质进行了研究,在416和438nm处观测到特别强的光发射,并对发射峰的来源进行了指认分析.与XRD数据计算得到的晶格参数相比,发现利用样品发光数据和公式Eem=-16963+164R,可以达到方便快捷地估算Mn-F之间距离和样品晶格常数的目的.     

The effect of annealing on the room temperature ferromagnetism in co-sputtered In2O3: C thin films

In this paper, we report investigation of room temperature (RT) ferromagnetism in In₂O₃ (InO) thin films doped with carbon prepared by the co-sputtering method. InO thin films both undoped and C doped with varied thicknesses in the range of 45 to 80 nm were synthesized on Si substrates with varied C concentrations. The carbon concentration was varied from 1.6 to 9.3 at%. The undoped InO films showed no trace of ferromagnetism. Carbon doped films (InO:C) exhibited ferromagnetism at RT, which was of the orders of 10⁻⁵ emu and varied strongly with C concentrations. It is observed that the magnetization reached a maximum value of 5.7 emu/cm³ at 4 at% C. Annealing of the InO:C films in an oxygen environment resulted in a decrease in the magnetization, indicating the crucial role of oxygen vacancies in the films. It is concluded that the oxygen vacancies were important and compete with C substitution for the RT ferromagnetism.     

Improved Handwritten Digit Recognition using Quantum K-Nearest Neighbor Algorithm

Handwritten numeral recognition is a technology for automatic recognition and classification of handwritten numeral input through machine learning model. This is widely used in postal code digital automatic system to sort letters. The classical k-nearest neighbor algorithm is used in the traditional digital recognition training model. The recognized digital image classification is obtained through similarity measure or calculation and K value selection. Nonetheless, as the applied data volume exceeds a certain threshold, the time complexity of the model increases exponentially upon the similarity measure and K value search. This condition makes it hard to apply the model universally. In this paper, we introduce quantum computing, that is where digital image information is stored in the quantum state, and its similarity is calculated in parallel. Also, the most similar K points are obtained through the Grover algorithm. The theoretical analysis of the proposed improved algorithm shows that, handwritten numeral recognition based on quantum k-neighbor algorithm can improved upon time complexity of \( \mathrm{O}\left(\mathrm{R}\sqrt{kM}\right) \) of the existing algorithm.

     

大啁啾光纤布拉格光栅的脉冲响应特性研究

脉冲堆积技术是高功率激光系统中产生任意种子脉冲的方案之一.该方案利用大啁啾光纤布拉格光栅的宽带特性来展宽宽带短脉冲,以满足脉冲堆积组件的需求.利用传输矩阵法模拟了大啁啾宽带光纤布拉格光栅的反射谱、时延曲线等特性.研究发现,光纤光栅的啁啾因子决定了色散量以及带宽的大小,但增加色散量的代价是降低了光纤光栅的带宽;光栅长度越长,反射带宽明显增加,但色散量变化不大.研究结果对高功率前端系统的设计具有一定的指导意义.     

Platinum clusters supported on/in Dion–Jacobson phase HLaNb<Subscript>2</Subscript>O<Subscript>7</Subscript> by topochemical method

Platinum clusters were supported on/in HLaNb₂O₇ nanosheets by topochemical reaction strategy for the first time. The as-prepared samples were analyzed using ICP OES and characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption–desorption isotherms and X-ray photoelectron spectroscopy. The results showed that HLaNb₂O₇ nanosheets were modified with platinum clusters with good monodispersity. The product was a mesoporous solid with broad pore size distribution and large surface area. The oxidation state of platinum was zero and the size of Pt clusters was only about 1–2 nm. This study provides a novel approach to support metal clusters on layered compounds.