Mn掺杂LiFePO4的第一性原理研究

采用基于密度泛函理论的第一性原理方法, 计算了不同Mn掺杂浓度LiFe_1-xMn_xPO₄ (x=0,0.25,0.50,0.75) 的电子结构. 同时采用流变相辅助高温固相碳热还原法制备了LiFe_1-xMn_xPO₄ (x= 0,0.25,0.50,0.75) 材料. 理论计算表明: LiFePO₄具有E_g = 0.725 eV的带隙宽度, 为半导体材料. 通过Fe位掺杂25%的Mn离子可最大程度地 减小材料带隙宽度、降低Fe---O键及Li---O键键能, 进而提高材料的电子电导率及锂离子扩散速率. 实验结果亦表明, 当Mn掺杂量x=0.25时, 材料具有最优的电化学性能, 其具有约为158 mAh· g^-1的放电比容量以及551 Wh· kg^-1的能量密度. 理论计算与实验结果非常符合.     

通过掺杂V和F提高碳包覆的磷酸铁锂锂离子电池的电化学性能

在原位聚合合成方法的基础上,结合两步烧结过程制得LiFe_1-xV_x(PO₄)_(3-y)/₃F_y/C.V和F掺杂对碳包覆的磷酸铁锂材料的结构、形貌和电化学性能有影响.通过XRD、FTIR、SEM、充/放电测试和电化学阻抗谱对材料的结构、形貌和电化学性能进行了表征.结果表明,V和F的掺杂并没有破坏橄榄石结构中的LiFePO₄/C,但可以提高晶体结构的稳定,降低电荷的转移阻抗,提高锂离子扩散速度,改善了LiFePO₄/C材料的循环性能和高倍率性能.     

针状纳米MnxNi0.5-xZn0.5Fe2O4的共沉淀法制备及表征

通过在碱液中共沉淀Mn²⁺、Ni²⁺和Fe²⁺后制备了棒状的前躯体,前躯体于不同温度煅烧后制得了Mn_xNi_0:5-xZn_0:5Fe₂O₄棒状体. 利用X射线衍射仪和透射电镜对棒状体的物相、形貌及粒径进行了表征,并利用振动样品磁强计对磁性能进行研究. 结果表明长径比大于15的棒状,随着x值的增加,Mn_xNi_0:5-xZn_0:5Fe₂O₄样品的直径增加,长度下降,长径比变小,当x=0.5时其直径在50 nm左右而长径比减小到7～8. 随着x值的增加,样品的矫顽力先增加后减少,x值达到0.4时样品的矫顽力再次增加,当煅烧温度为600 oC,x=0.5时样品的矫顽力最大为134.3 Oe. 饱和磁化强度随着x值的增加先增加后减少,当煅烧温度为800 oC和x=0.2时达到最大为68.5 Oe.     

用于电压基准的Nb/NbxSi1-x/Nb约瑟夫森单结的研制

现代可编程约瑟夫森电压基准的核心器件是约瑟夫森结阵.目前最具有优势的约瑟夫森结阵是 Nb/Nb_xSi_1-x/Nb材料的结阵. Nb/Nb_xSi_1-x/Nb材料的约瑟夫森结 具有三层薄膜的制作过程简便, Nb和Nb_xSi_1-x刻蚀工艺相同以及Nb_xSi_1-x 势垒层成分可调等优点.中国计量科学研究院设计制作了Nb/Nb_xSi_1-x/Nb约瑟夫森单结. 通过在4.2 K低温下对所做单结进行直流电流-电压特性测量,观测到了清晰的超导隧穿电流和 从零电压态向电压态的跳变,最后就测量结果进行了分析讨论.此项工作属于国内首个开展 Nb/Nb_xSi_1-x/Nb材料约瑟夫森单结研究的工作.     

钴改性Fe3O4-MnO2催化转化生物质合成气制备液体燃料

本文制备了用于费托合成反应的钴改性Fe₃O₄-MnO₂双功能催化剂,并探究了钴负载量对Fe-Co协同效应的影响以及Fe₁Co_xMn₁催化剂的费托合成反应性能. 实验发现,在Fe₃O₄-Mn催化剂中加入Co可促进铁氧化物的还原、增加反应过程中铁位点的活性. 此外,Co的加入可增强Fe-Co金属间的电子转移,加强两者的协同作用,提高催化性能. Co负载较高的Fe₁Co_xMn₁催化剂可进一步促进加氢反应能力,使产品分布向短链烃方向转移. 在280 ^°C、2.0 MPa和3000 h^-1的最佳工况条件下,Fe₁Co₁Mn₁催化剂的液体燃料收率最高.     

Hg1-xCdxTe的共振拉曼散射

当入射光的光子能量接近Hg_1-xCd_xTe的E₀+Δ₀时,发现了Hg_1-xCd_xTe的共振拉曼散射,观察到了“禁戒”共振增强拉曼散射,同时也观察到了二级共振拉曼散射.分析了非共振条件下能在样品的(100)面观察到微弱的“禁戒”TO₂模以及在共振条件下“禁戒”TO₂模大大增强的原因.通过分析,发现由双LO声子引起的二级共振拉曼散射主要     

MnxSny(x=2,3,4; y=18,24,30)团簇几何结构的密度泛函研究

采用密度泛函方法,研究了Mn_xSn_y(x=2,3,4; y=18,24,30)团簇的几何结构. 发现Mn_xSn_6x+6(x=2,3,4)倾向于形成 Mn 原子内掺入D_3d Sn团簇单笼结构,即Mn₂Sn₁₈, Mn₃Sn₂₄ 和Mn₄Sn₃₀.而Mn_xSn_6x+12(x=2,3)则倾向于形成由两个小笼连接 而成的双笼结构,即MnSn₁₂-MnSn₁₂ 和MnSn₁₂-Mn₂Sn₁₈.因此,可望通过控制掺杂Mn 原子的数量来组装成不同结构的Mn_xSn_y一维纳米线.     

Mn4+掺杂对BiFeO3陶瓷微观结构和电学性能的影响研究

利用传统的固相反应法制备了BiFe_1-xMn_xO₃ (x= 0-0.20)陶瓷样品, 研究了不同Mn⁴⁺掺杂量对BiFeO₃陶瓷密度、物相结构、显微形貌、 介电性能和铁电性能的影响.实验结果表明:所制备的BiFe_1-xMn_xO₃ 陶瓷样品的钙钛矿主相均已形成,具有良好的晶体结构, 且在掺杂量x=0.05附近开始出现结构相变.随着Mn⁴⁺添加量的增加, 体系的相结构有从菱方钙钛矿向斜方转变的趋势,且样品电容率大幅度增大, 而介电损耗也略有增加;在测试频率为10⁴ Hz条件下, BiFe_0.85Mn_0.15O₃ (ε_r=1065)的 ε_r是纯BiFeO₃ (ε_r=50.6)的22倍; 掺杂后样品的铁电极化性能均有不同程度的提高,可能是由于Mn⁴⁺稳定性优于 Fe³⁺,高价位Mn⁴⁺进行B位替代改性BiFeO₃陶瓷, 能减少Bi³⁺挥发,抑制Fe³⁺价态波动,从而降低氧空位浓度,减小样品的电导和漏电流.     

Si1-xGex合金半导体中CiCs和CiOi缺陷随Ge含量的变化

采用从头计算(ab initio)的方法对Si和Si_1-xGe_x合金半导体材料中C_iC_s缺陷的性质进行探讨，同时也对比调查了C_iO_i缺陷在Si和Si_1-xGe_x合金中的性质. 在不同Ge含量的Si_1-xGe_{x相似文献}   

Co1-xMnx合金电子结构和磁性的理论研究

Co_1-xMn_x合金的磁性强烈地依赖于其结构以及Mn的相对含量.从第一性原理出发,用线性缀加平面波(LAPW)方法,分别计算了x=0.00,0.25,0.50,0.75,1.00的情况下,面心立方(fcc)和体心立方(bcc)结构的Co_1-xMn_x合金的电子结构和基态磁性.随x的增大,fcc结构的Co_1-xMn_x合金的磁性从铁磁性和亚铁磁性变为反铁磁性;bcc结构Co相似文献   

Insertion properties of LiFe<Subscript>0.5</Subscript>Mn<Subscript>0.5</Subscript>PO<Subscript>4</Subscript> electrode materials for Li-ion batteries

This paper addresses the synthesis structural and electrochemical properties of LiFe_0.5Mn_0.5PO₄ electrode materials for Li-ion batteries. The charge–discharge reaction of Li/LiPF₆-EC–DEC/LiFe_0.5Mn_0.5PO₄ cell carried out at the 1-C rate shows a capacity retention of 128 mAh/g. The local structure of the delithiated Li _x Fe_0.5Mn_0.5PO₄ phases have been studied by Fourier transform infrared spectroscopy and magnetometry. Spectral features indicate that the structure of the delithiated phase remains in the orthorhombic system. The compositional dependence of the magnetic moment is found to be in quantitative agreement with the theoretical value predicted for oxidation of M ²⁺ ions in the high spin state. Paper presented at the 11th Euro-Conference on Science and Technology of Ionics, Batz-sur-Mer, France, 9–15 Sept. 2007     

The crystal structures and physical properties of the solid solution compound Ba5Y8-xMn4O21-1.5x (x=0, 1)

New oxometallides with the formula Ba5Y8 xMn4O21 1.5x(x = 0,1) are prepared through an atmospherecontrolled solid-state reaction.Two single-phase samples with Ba/Y/Mn atomic ratios 5/8/4(Y8) and 5/7/4(Y7) are obtained.The crystal structures and the physical properties of the compounds are investigated by X-ray powder diffraction,magnetization,conductivity,and dielectricity measurements.The Ba5Y8 xMn4O21 1.5x compound is demonstrated to be a Y-deficient solid solution.The solid solution compound Ba5Y8 xMn4O21 1.5x crystallizes into tetragonal symmetry with the space group I4/m.Detailed structure analysis by Rietveld refinement of the X-ray powder diffraction data reveals that the Y vacancies occur preferentially at the Y(2) site.Thermal magnetization measurements indicate the presence of antiferromagnetic interaction between Mn ions in the compounds,and temperature-dependent resistivity measurements show that insulator-semiconductor transitions occur around 175 K and 170 K for the Y8 and Y7 samples,respectively.Strong frequency dependences of the dielectric constant are observed above ～175 K for the two compounds.     

Hydrothermal synthesis and properties of manganese-doped LiFePO4

A series of carbon-coated LiFe_1???x Mn _x PO₄ compounds are prepared by a hydrothermal method at 170 °C for 12 h. The structure and morphology of the prepared composites are characterized to examine the effects of Mn²⁺ substitution. All LiFe_1???x Mn _x PO₄ compositions are found to have an ordered olivine-type structure with homogeneous Fe²⁺ and Mn²⁺ distributions. The substitution leads to grain refinement from ~500 to ~150 nm, as well as to increased initial capacity and improved electronic conductivity. The amount of carbon coating varies with increased doping amount. The discharge curves of the LiFe_1???x Mn _x PO₄/C materials reveal a high discharge plateau corresponding to Fe^2+/3+ and no obvious plateau assigned to Mn^2+/3+, although a slight contribution of manganese is detected. However, the electrochemical performance, including the discharge capacity and cyclic performance, deteriorates with increased Mn content in the composite.     

Er2AlFe16－xMnx化合物的磁性及反常热膨胀

通过X射线衍射及磁测量手段研究了Er₂AlFe_16-xMn_x(x=1，2，3，4，6，8)化合物的结构和磁性. 研究结果表明Er₂AlFe_16-xMn_x化合物具有六角相的Th₂Ni₁₇型结构. 采用X射线热膨胀测定法在103—654K的温度范围内测量了Er₂AlFe_16-xMn_x(x=1，2，3，4)化合物的热膨胀性质，发现这些化合物在低温下存在热膨胀反常现象，在居里点附近具有负膨胀性质. 对自发磁致伸缩的研究结果表明Er₂AlFe_16-xMn_x化合物中存在着较强的各向异性的自发磁致伸缩，低温下自旋重取向的出现使得化合物的自发体磁致伸缩有所增强. 磁测量结果表明Mn的替代导致Er₂AlFe_16-xMn_x化合物的居里温度及自发磁化强度急剧下降，并且使得化合物的磁晶各向异性发生显著改变. 关键词： 2AlFe_16-xMn_x化合物')" href="#">Er₂AlFe_16-xMn_x化合物 反常热膨胀 自发磁致伸缩     

Recent advances on Fe- and Mn-based cathode materials for lithium and sodium ion batteries

The ever-growing market of electrochemical energy storage impels the advances on cost-effective and environmentally friendly battery chemistries. Lithium-ion batteries (LIBs) are currently the most critical energy storage devices for a variety of applications, while sodium-ion batteries (SIBs) are expected to complement LIBs in large-scale applications. In respect to their constituent components, the cathode part is the most significant sector regarding weight fraction and cost. Therefore, the development of cathode materials based on Earth’s abundant elements (Fe and Mn) largely determines the prospects of the batteries. Herein, we offer a comprehensive review of the up-to-date advances on Fe- and Mn-based cathode materials for LIBs and SIBs, highlighting some promising candidates, such as Li- and Mn-rich layered oxides, LiNi_0.5Mn_1.5O₄, LiFe_1-xMn_xPO₄, Na_xFe_yMn_1-yO₂, Na₄MnFe₂(PO₄)(P₂O₇), and Prussian blue analogs. Also, challenges and prospects are discussed to direct the possible development of cost-effective and high-performance cathode materials for future rechargeable batteries.     

预注入对Si1-xCx合金形成的影响

室温下在单晶Si中注入(0.6—1.5)at%的C原子,部分样品在C离子注入之前在其中注入²⁹Si⁺离子产生损伤,然后在相同条件下利用高温退火固相外延了Si_1-xC_x合金,研究了预注入对Si_1-xC_x合金形成的影响.如果注入C离子的剂量小于引起Si非晶化的剂量,在950℃退火过程中注入产生的损伤缺陷容易与C原子结合形成缺陷团簇,难于形成Si_1-xC关键词： 离子注入 固相外延 1-xC_x合金')" href="#">Si_1-xC_x合金     

Preparation, structure and ferromagnetic properties of the nanocrystalline Ti1-xMnxO2 thin films grown by radio frequency magnetron co-sputtering

This paper reported that the Mn-doped TiO2 films were prepared by radio frequency （RF） magnetron cosputtering. X-ray diffraction measurements indicate that the samples are easy to form the futile structure, and the sizes of the crystal grains grow big and big as the Mn concentration increases. X-ray photoemlssion spectroscopy measurements and high resolution transmission electron microscope photographs confirm that the manganese ions have been effectively doped into the TiO2 crystal when the Mn concentration is lower than 21%. The magnetic property measurements show that the Ti1-xMnxO2 （x = 0.21） films are ferromagnetic at room temperature, and the saturation magnetization, coercivity, and saturation field are 16.0 emu/cm^3, 167.5 × 80 A/m and 3740 × 80 A/m at room temperature, respectively. The room-temperature ferromagnetism of the films can be attributed to the new futile Ti1-xMnxO2 structure formed by the substitution of Mn^4＋ for Ti^4＋ into the TiO2 crystal .lattice, and could be explained by O vacancy （Vo）-enhanced ferromagnetism model.     

Mn替代对Dy2AlFe16－xMnx化合物的结构和磁性的影响

通过X射线衍射及磁测量手段研究了Dy₂AlFe_16-xMn_x化 合物的结构和磁性.研究结果表明Dy₂AlFe_16-xMn_x化合 物具有六角相的Th₂Ni₁₇型结构.对x=1，2的样品采用X射线热膨胀 测定法在104—647K的温度范围内测量了其热膨胀性质，发现这些化合物在低温下存在热膨 胀反常现象，在居里点附近出现负膨胀性质.对自发磁致伸缩的研究结果表明Dy₂AlFe_16-xMn_x化合物中存在着较强的各向异性的自发磁致伸缩，随 着Mn含量的增加，其低温下的自发体磁致伸缩减弱.磁测量结果表明Mn的替代导致Dy_{2< /sub>AlFe16-xMnx化合物的居里温度及自发磁化强度急剧下降. 关键词： 2}AlFe_16-xMn_x化合物')" href="#">Dy₂AlFe_16-xMn_x化合物 反常热膨胀 自发磁致伸缩 自发磁化强度     

TiN和Ti1-xSixNy薄膜的微观结构分析

使用x射线衍射(XRD)、x射线光电子谱(XPS)、高分辨透射电子显微镜(HRTEM)和原子力显微镜（AFM）多种观测手段分析了TiN薄膜和Ti_1-xSi_xN_y纳米复合薄膜的微观结构.实验分析证明Ti_1-xSi_xN_y薄膜是由直径为3—5nm的纳米晶TiN和非晶Si₃N₄相构成，并且Ti_1-xSi_{x关键词： 纳米复合薄膜 自由能 表面粗糙度 TiN 1-x}Si_xN_y')" href="#">Ti_1-xSi_xN_y