Er3(Fe,Co,M)29化合物(M=Cr,V,Ti,Mn,Ga,Nb)的结构与磁性

合成了Er3Fe29-x-yCoxMy化合物(M=Cr,V,Ti,Mn,Ga,Nb)并用x射线衍射和磁测量等手段研究了它们的结构和磁性.发现Fe基Er3(Fe,M)29化合物结晶成哑铃对Fe-Fe无序替代的Th2Ni17型结构(P63/mmc空间群)而不能形成Nd3(Fe,Ti)29型结构,因此其化学式也可以用Er2-n(Fe,M)17+2n(n=0.2)表示.当Er3Fe29化合物中部分Fe原子被M原子所取代时,其居里温度均有一定程度的提高.所有Er3(Fe,M)29化合物在室温均为易面型各向异性.当Er3(Fe,M)29(M=Cr,V)中的部分Fe原子被Co原子取代且Co原子数与Fe原子数达到一定比值时,得到一个单斜结构的新相.磁测量表明Er3Fei95Co6V3.5在室温可能为单轴各向异性,在162K出现自旋重取向,其各向异性由易轴型变为易面型.在5K下于难磁化方向磁化时观察到一个一级磁化过程(FOMP).     

In2（MoO4)3晶体的高压拉曼振动研究

钼酸铟(In2(MoO4)3)由于其独特的负热膨胀性质,已被广泛应用于燃料电池、光学器件、激光材料等方面. 为了进一步探讨其晶体结构和物理性质,本工作在金刚石对顶砧上原位测量了In2(MoO4)3 的高压拉曼光谱,最高压力达到18 GPa. 在研究的压力范围内,本工作观察到了两次相变. 首先,In2(MoO4)3在压力为1.2 GPa 时, 发生了 由从P21/a相到低对称结构的相转变. 在压力为5.8 GPa 时, 样品又发生了从晶相到非晶相的第二次相转变. 卸压后样品仍为非晶相,说明In2(MoO4)3 在高压下的非晶相变为不可逆相变.      

(K,Mo)Y分子筛中钼组分的EXAFS研究

应用同步辐射Eextended X-ray Ab sorption Fine S tructure(EXAFS)技术研究固态法制备的KHMoY分子筛的氧化态和硫化态样品以及硫化态KHY／MoO3样品中钼组分的局域配位环境结构,并与KHMoY和KHY／MoO3 样品催化加氢活性结果进行对照。结果表明,随原子比（K＋2Mo）／Al的变化,钼原子周围的配位环境有显著的差异。当（K＋2Mo）／Al时,KHMoY和KHY/MoO3硫化后,钼组分主要以MoS2小原子簇分散在分子筛超笼中;（K＋2Mo)/Al>1时,钼组分则有两种存在环境,即分子筛超笼中的和分子筛外表的钼组分。分子筛超笼中的Mo S2原子簇的催化加氢合成醇选择性较高;分子筛外表面的MoS2微小颗粒的尺寸相对于超笼中的要大许多,其合成醇选择 性较低。     

The phase transition,hygroscopicity, and thermal expansion properties of Yb_2-xAl_xMo₃O₁₂

Materials with the formula Yb 2-xAlxMo3O12(x =0.1, 0.2, 0.3, 0.4, 0.5, 0.7, 0.9, 1.0, 1.1, 1.3, 1.5, and 1.8) were synthesized and their structures, phase transitions, and hygroscopicity investigated using X-ray powder diffrac- tion, Raman spectroscopy, and thermal analysis. It is shown that Yb2-xAlxMo3O12 solid solutions crystallize in a single monoclinic phase for 1.7 ≤ x ≤ 2.0 and in a single orthorhombic phase for 0.0 ≤ x ≤ 0.4, and exhibit the characteristics of both monoclinic and orthorhombic structures outside these compositional ranges. The monoclinic to orthorhombic phase transition temperature of Al2Mo3O12 can be reduced by partial substitution of Al 3+ by Yb3+, and the Yb2-x AlxMo3O12 (0.0 < x ≤ 2.0) materials are hydrated at room temperature and contain two kinds of water species. One of these interacts strongly with and hinders the motions of the polyhedra, while the other does not. The partial substitution of Al3+ for Yb3+ in Yb2Mo3O12 decreases its hygroscopicity, and the linear thermal expansion co- efficients after complete removal of water species are measured to be 9.1×10 6 /K, 5.5×10 6 /K, 5.74×10 6 /K, and 9.5 × 10 6 /K for Yb1.8 Al0.2 (MoO4)3 , Yb1.6Al0.4 (MoO4 )3, Yb0.4 Al1.6 (MoO4)3 , and Yb 0.2Al1.8 (MoO4)3 , respectively.     

Fe2-xYxMo3O12系列材料的相变及负膨胀性研究

本文对Fe2-xYx(MoO4)3(x=0.0,0.2,0.4,0.5,0.6,0.8,1.0,1.2,1.4,1.6,1.8,2.0)系列材料的相变及负膨胀性能进行了研究.通过对Fe2-xYx( MoO4)3系列材料的XRD和拉曼谱的分析发现,当x≤0.4时Fe2-xYxMo3O12在常温下是单斜结构;当x≥0.5时...     

基质发光材料Na5Eu(MoO4)4和NaEu(MoO4)2的制备和发光

本文研究了化学计量的基质发光材料Na5Eu(MoO4)4和NaEu(MoO4)2.它们都属于四方晶系,空间群为I41/α .NaEu(Mo04)2属于白钨矿(scheelite)结构,一个晶胞中有2个分子式NaEu(MoO4)2(z=2);而Na5Eu(Mo4O)4属于类自钨矿(scheelite-like)结构,一个晶胞中有4个分子式Na5Eu(MoO4)4(z=4).X射线衍射确定的晶胞常数,对Na5Eu(MoO4)4,α=1.1439nm和c=1.1486nm(密度d计算=4.01g/cm3,z=4);对NaEu(MoO4)2,α=0.5236nm和c=1.1439nm(密度d计算=5.24g/cm3,z=2).由差热法和X射线衍射法确定了Na2MoO4-Eu2(MoO4)3的相图.Na5Eu(MoO4)4分解为NaEu(MoO4)2的温度是700℃.本文确定了制备纯 Na5Eu(MoO4)和NaEu(MoO4)2的方法,并研究了上述两种材料的激发光谱和发光光谱.确定了用X射线粉末衍射谱和发光光谱鉴别Na5Eu(MoO4)4和NaEu(MoO4)2的方法.在365nm紫外光激发下,Na5Eu(MoO4)4的发光比Na5Eu(WO4)4的强得多,在室温下,Na5Eu(MoO4)4,NaEu(MoO4)2和Na5Eu(WO4)4的相对发光积分亮度比为3.8:3.2:1.0.     

Er3(Fe,Co, M)29化合物(M=Cr,V, Ti,Mn, Ga,Nb)的结构与磁性

合成了Er_３Fe_29-x-yCo_xM_y化合物(M=Cr, V, Ti, Mn, Ga, Nb )并用x射线衍射和磁测量等手段研究了它们的结构和磁性. 发现Fe基Er_３(Fe,M)_２９化合物结晶成哑铃对Fe-Fe无序替代的Th₂Ni₁₇型结构(P6₃/mmc空间群)而不能形成Nd₃(Fe,Ti)_２９型结构，因此其化学式也可以用Er_2－n(Fe,M)_17+2n (n=0.2)表示. 当Er_３Fe₂₉化合物中部分Fe原子被M原子所取代时，其居里温度均有一定程度的提高. 所有Er_３(Fe,M)_２９化合物在室温均为易面型各向异性. 当Er_３(Fe,M)_２９ (M=Cr, V)中的部分Fe原子被Co原子取代且Co原子数与Fe原子数达到一定比值时，得到一个单斜结构的新相. 磁测量表明Er_３Fe_19.5Co₆V_3.5在室温可能为单轴各向异性，在162K出现自旋重取向，其各向异性由易轴型变为易面型. 在5K下于难磁化方向磁化时观察到一个一级磁化过程(FOMP). 关键词： 稀土金属间化合物 晶体结构 磁晶各向异性     

基质发光材料Na5Eu(MoO4)4和NaEu(MoO4)2的喇曼光谱

本文研究了基质发光材料Na5Eu(MoO4)4和NaEu(MoO4)2的喇曼光谱.用群论方法分析了它们的内、外振动模式,对实验振动模进行了指认.本文还将上述喇曼光谱与Na5Eu(WO4)4、CaWO4、SrWO4、CaMoO4和SrMoO4的喇曼光谱进行了比较,Na5Eu(MoO4)4和NaEu(MoO4)2的喇曼光谱结果表明(MoO4)2-离子团的高能量拉伸内振动是产生Eu3+的5D2→5D1,5D1→5D0-多声子无辐射弛豫的原因,这导致了Eu3+在这类材料中主要产生5DO→7Fj的发光跃迁.     

K7[P2Mo4W13M(H2O)O61]及其有机复合材料的合成及光谱研究

用降解法制得了Dawson结构铬、铁取代的磷钼钨酸钾,并将其与溴化(E)-N-丁基-4-(2-(4-二甲氨基苯基)乙烯基)吡啶反应制备了有机复合材料.通过元素分析和TG-DTA确定了配合物的组成分别为K7[P2Mo4W13M(H2O)O61](M=Cr(1),Fe(2))和(C19H25N2)6K3[P2Mo4W13MO62](M=Cr(3),Fe(4)).利用红外光谱、紫外-可见光谱、固体漫反射紫外-可见-近红外光谱、X射线光电子能谱以及荧光光谱对上述化合物进行了表征,并研究了复合材料中无机与有机组分间的相互作用及其荧光性质.     

密度泛函理论研究混合团簇Al12X(X=Sc、Ti、V、Gr、Mn、Fe、Co、Ni、Cu、Zn)的结构和磁性

以四种13原子高对称性(Ih、Oh、D5h、D3h)密堆积结构为初始构型,通过不等价位原子替换,利用密度泛函理论系统研究了Al12 X(X=Sc、Ti、V、Cr、Mn、Fe、Co、Ni、Cu、Zn)掺杂团簇的结构及磁性.结果表明:除Al12 Cr和Al12Fe以外,其它Al12X团簇的基态结构均以Ih替换结构为主,其中前3d元素(X=Sc、Ti、V、Mn)倾向于表面位置替换,而后3d元素(X=Co、Ni、Cu、Zn)则倾向于中心位置替换;Al12 Cr和Al12Fe团簇以Oh结构的表面替换为基态结构;对多数3d元素(X=Ti、V、Cr、Fe、Co、Zn)其掺杂团簇均出现明显的近能同分异构现象;相较纯Al13团簇掺杂团簇普遍体现出磁性增强效应.     

新型红色荧光粉NaLa_(0.7)(MoO_4)_(2-x)(WO_4)_x∶0.3Eu~(3+)的制备及发光性质研究

采用高温固相法合成具有余辉性能的发光材料NaLa_(0.7)(MoO_4)_(2-x)(WO_4)_x∶0.3Eu~(3+)(x=0,0.5,1,1.5,2)。用X射线衍射(XRD)和荧光光谱对样品的晶体结构和发光特性进行表征。测试结果表明,在900℃下烧结8 h所合成的NaLa_(0.7)(MoO_4)_(2-x)(WO_4)_x∶0.3Eu~(3+)样品为纯相Na La(Mo O_4)_2,样品可被近紫外光393nm和蓝光462 nm有效激发,其发射主峰位于615 nm处,属于Eu3+的5D0-7F2跃迁。Na La_(0.7)(Mo O_4)_(2-x)-(WO_4)_x∶0.3Eu~(3+)的发光强度随着W6+浓度的增加而增大,当W6+掺杂量x=1时发光最强,而后随W6+掺杂浓度的增加出现浓度猝灭现象。通过计算得到样品在393 nm和462 nm激发下的色坐标,当W6+的掺杂量x=1时,样品的红光色纯度最好。     

LED用红色发光材料 Li3Ba2Ln3-xEux(MoO4)8的制备及性能

采用溶胶-凝胶法合成了发光二极管(LED)用的系列红色荧光粉Li₃Ba₂Ln_3-xEu_x(MoO₄)₈ (Ln=La, Gd, Y)。利用差热-热重(TG-DTA)分析和粉末X 射线衍射(XRD)测定了其最佳合成温度和不同温度下所得样品的结构,发现所有样品均具有单斜结构;采用荧光光谱对所得荧光粉发光性能进行了表征,发现在相同条件下所得样品的发光强度顺序为:Li₃Ba₂Y_2.8Eu_0.2(MoO₄)₈＞Li₃Ba₂Gd_2.8Eu_0.2(MoO₄)₈＞Li₃Ba₂La_2.8Eu_0.2-(MoO₄)₈。它们在395 nm和465 nm的激发光源激发时均有强的吸收,与LED芯片发射波长相匹配。同时分析了柠檬酸及分散剂聚乙二醇(PEG-10000)的用量、Eu³⁺离子的浓度以及焙烧温度等因素对荧光粉发光性能的影响。     

Initial oxidation stages on FeCr(100) and FeCr(110) surfaces

Simultaneous LEED and AES are used to follow early stages of oxidation of monocrystalline FeCr(100) and (110) between 700 and 900 K in the oxygen pressure range 10^?9–10^?6 Torr. A chromium-rich oxide region at the alloy/oxide interface is observed, which exhibits different surface structures on oxidized FeCr(100) and FeCr(110). The chromium concentration in this initially formed oxide film is found to be enhanced by low oxygen pressures or high temperatures. During further oxidation different behaviours are observed on FeCr(100) and FeCr(110), which are explained by assuming different ion permeabilities through the initial chromium rich oxide regions on the two surface planes. On FeCr(110) surfaces oxidation is initiated on chromium enriched (100) facets at 800 K or below. At 900 K a film consisting of rhombohedral Cr₂O₃ or (Fe, Cr)₂O₃ is epitaxially growing with its (001) plane parallel to the alloy (110) face. On FeCr(100) surfaces the chromium rich oxide region next to the substrate is of fcc type. As soon as the diffusion of iron from the alloy to the gas/oxide interface is observable, a spinel type oxide is formed and connected with the location of iron in tetrahedral lattice sites. Closer to the fcc lattice the spinel oxide consists of FeCr₂O₄ or a solid solution of FeCr₂O₄ and Fe₃O₄ whereas next to the gas phase the oxide is pure Fe₃O₄.     

Ab Initio Study of NaMFe(MoO4)3 (M = Mn,Fe, Co,Ni, Zn): Electron Structure,Sodium Diffusion and Potentials

Physics of the Solid State - The electronic structures of NaMFe(MoO4)3 (M = Mn, Fe, Co, Ni, Zn) molybdates isostructural to α-NaFe2(MoO4)3 or β-NaFe2(MoO4)3 is studied. Taking into...     

Structure, spin reorientation and M(o)ssbauer effect studies of Tb0.3Dy0.7(Fe1-xAlx)1.95 alloys

The effect of Al substitution for Fe on crystal structure, magnetostriction and spontaneous magnetostriction, anisotropy and spin reorientation of a series of polycrystalline Tb0.3Dy0.7(Fe1-xAlx)1.95 alloys (x = 0, 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, 0.35) at room temperature and 77 K was investigated systematically. It was found that the primary phase of Tb0.3Dy0.7(Fe1-xAlx)1.95 is the MgCu2-type cubic Laves phase structure when x < 0.4 and the lattice constant a of Tb0.3Dy0.7(Fe1-xAlx)1.95 increases approximately and monotonically with the increase of x. The substitution of Al leads to the fact that the magnetostriction ( inceases slightly in a low magnetic field (H ≤ 40 kA/m), but decreases sharply and is easily close to saturation in a high applied field as x increases, showing that a small amount of Al substitution is beneficial to a decrease in the magnetocrystalline anisotropy. It was also found that the spontaneous magnetostriction (ζ)111 decreases greatly with x increasing. The analysis of the M(o)ssbauer spectra indicated that the easy magnetization direction in the {110} plane deviates slightly from the main axis of symmetry with the changes of composition and temperature, namely spin reorientation. A small amount of non-magnetic phase exists for x = 0.15 in Tb0.3Dy0.7(Fe1-xAlx)1.95 alloys and the alloys become paramagnetic for x > 0.15 at room temperture, but at 77 K the alloys still remain magnetic phase even for x = 0.2. At room temperature and 77 K, the hyperfine field decreases and the isomer shifts increase with Al concentration increasing.     

Epitaxial growth and magnetic exchange anisotropy in Fe3O4<Emphasis Type="Bold">/NiO bilayers grown on MgO(001) and Al</Emphasis>2O3(0001)

Epitaxial Fe3O4/NiO bilayers were epitaxially grown on MgO(001) and Al2O3(0001) substrates to investigate the influence of the fully spin compensated (001) and the non-compensated (111) NiO interface planes between the ferromagnetic (F) and antiferromagnetic (AF) layers on the AF/F exchange coupling. Bilayers of different magnetite thicknesses and constant NiO thickness were investigated. The structural characterizations indicate a perfect epitaxy of the two layers for the both growth directions in the two Fe3O4/NiO/MgO(001) and NiO/Fe3O4/Al2O3(0001) systems. An epitaxial ferrimagnetic (Ni,Fe)Fe2O4 phase is observed at the AF/F interface when the NiO oxide is grown on the top of the Fe3O4 layer while a perfectly flat AF/F interface is observed in the Fe3O4/NiO/MgO(001) system exhibiting only a very slight interdiffusion. Magnetic measurements indicate a relative strong bias at 300 K for the bilayers grown on Al2O3(0001), which decreases with the inverse of the ferrimagnetic layer thickness as theoretically expected. On the contrary, a zero exchange biasing is observed at 300 K for the bilayers grown on MgO(001).     

Cr、Mn、Co、Ni掺杂对Al13Fe4相稳定性和力学性能影响的第一性原理研

采用基于密度泛函理论的第一性原理计算方法,系统地研究了不同掺杂浓度下过渡族元素Cr、Mn、Co、Ni在Al13Fe4相中的占位情况、结构稳定性和机械性能. 计算得到所有的Al13(Fe24-xMx) (M=Cr、Mn、Co、Ni;X=1,2,4)相都具有良好的热力学稳定性和机械稳定性. 相同掺杂浓度化合物的形成焓按如下顺序减小：Al78(Fe24-xCrx) > Al78(Fe24-xMnx) > Al13Fe4 > Al78(Fe24-xNix) > Al78(Fe24-xCox).形成焓的降低增加了Al13Fe4相成核驱动力,Co和Ni有利于促进Al-Fe合金中Al13Fe4相形核,细化Al13Fe4相. 过渡族元素可以改善金属间化合物的脆性,增强塑性变形能力. 并且随着掺杂浓度的增加,过渡族元素的加入对脆性的改善呈先增大后减小的趋势.     

高重复频率飞秒脉冲激光诱导钼酸镝玻璃表面析出β′-Dy2（MoO4）3和α-MoO3晶体

高重复频率飞秒脉冲激光辐照钼酸镝玻璃表面后,通过显微拉曼测试,发现在辐照区域内形成了含有MoO4四面体结构的β′-Dy2(MoO4)3晶体和含有MoO6八面体结构的α-MoO3晶体。通过电子能谱(EDS)测量辐照前后样品中钼(Mo)元素的含量,发现在辐照中心位置形成α-MoO3晶体相的区域内出现了明显的Mo元素缺失现象,表明了在高温场作用下,微爆现象引起了材料中心密度的降低。此外,随着辐照时间的增加辐照中心位置还出现了由Dy2(MoO4)3相向MoO3晶体α相的相变。这说明随着激光作用程度的加剧,中心区域Mo元素浓度降低,使得钼氧结构由MoO4四面体向MoO6八面体转变,导致在Mo元素浓度较低的区域更容易形成八面体结构的α-MoO3。