La2/3(Ca60Ba40)1/3MnO3的磁电阻与磁化强度及其相关性

用固相反应法制备了La2/3(Ca60Ba40)1/3MnO3多晶材料,测量了77K～320K范围内的磁化曲线及在77K～350K范围内0～1.0T外磁场下的电阻率。结果表明低场磁电阻与高场磁电阻随外磁场的变化与磁化强度(M2)的变化存在着一定相关性,采用ρ(M)∝1-M2及低温隧穿磁电阻效应和逾渗模型解释了实验结果。     

改善钙钛矿材料室温下磁电阻效应的有效途径

将Ag2O与La0.67Ca0.25Sr0.08MnO3均匀混合经高温烧结后形成La0.67Ca0.25Sr0.08MnO3/xAg两相复合体系。随Ag掺入量的增加,样品的电阻率明显下降,磁化强度有小量下降,TC及电阻率的峰值温度TP没有明显变化。304K温度下,从x=0.25样品中得到最大磁电阻效应,磁电阻比约为41%,分别是La0.67Ca0.25Sr0.08MnO3和La0.67Sr0.33MnO3样品的1.6及10倍。磁电阻的本征效应和传导电子在界面处的自旋相关散射作用是产生室温下增强磁电阻效应的主要原因。结果说明,利用离子的掺杂效应调整居里温度到室温附近,再结合金属/钙钛矿复合体系界面属性丰富的特性来制备庞磁电阻材料是提高室温磁电阻有效的途径,这对应用研究具有十分重要的意义。     

La_(0.80)Sr_(0.05)Na_(0.15)MnO_3/xCuO复合体电输运机制及磁电阻的温度稳定性

用固相反应法制备了La0.80Sr0.05Na0.15MnO3/xCuO(x=0,0.05,0.10,0.15,0.20,0.30)二相复合体系,通过X射线衍射(XRD)图谱、电阻率-温度(ρ-T)曲线、ρ-T拟合曲线、磁电阻-温度(MR-T)曲线,研究了样品的电输运机制及磁电阻的温度稳定性。结果表明,在低温类金属区,电输运机制是自旋电子受单磁子散射作用,用ρ-T2拟合得很好;在较高温区MR-T曲线出现"压峰效应",是因为界面效应产生的非本征磁电阻占优势,本征磁电阻与非本征磁电阻迭加产生的磁电阻随温度变化不大;特别是x=0.05的样品,0.8 T磁场下在240 K~320K温区,磁电阻保持(9.9±0.4)%基本不随温度变化,在室温附近△T=80 K温区磁电阻的温度稳定性很好。     

La2/3(CaXBa1-X)1/3MnO3材料的绝缘体-金属转变与晶界效应

用固相反应法制备了La2/3(CaxBa1-x)1/3MnO3(x=0.00,0.40,0.45,0.55,0.60,1.00)六种多晶CMR材料,并测量了在77K～350K范围内零磁场和0.4T外磁场下的电阻率。这些样品都出现了双电阻峰结构,采用Mott转变表达式ρ～exp(T0/T)1/4拟合了实验数据,结果表明高温峰的转变是绝缘体-金属(I-M)转变,而低温峰不是I-M转变峰,用自旋极化电子隧道效应和局域化模型解释了电阻和磁电阻行为。此外,在x=0.4～0.6掺杂范围内样品呈现出异常的电阻行为。     

CuO复合对La0.80Sr0.05K0.15MnO3电输运和磁电阻的影响

用固相反应法制备了(1-x)La0.80Sr0.05K0.15MnO3/xCuO(x=0.00,0.04,0.08,0.10,0.20,0.30)二相复合体。通过X射线衍射图谱、扫描电子显微镜照片检测结构,表明形成完好的钙钛矿相和CuO相,CuO分布在钙钛矿颗粒之间,形成对钙钛颗粒的包覆。通过测量零场和加场下的电阻率-温度曲线以及磁电阻-温度曲线,研究电输运性质及磁电阻效应,结果表明,CuO复合对La0.80Sr0.05K0.15MnO3电输运和磁电阻效应影响很大。在高温区出现磁电阻峰,表现出本征磁电阻特征,在低温区随温度降低磁电阻持续增大,表现出由界面引起的隧穿磁电阻特征,总的磁电阻是本征磁电阻与隧穿磁电阻的迭加,在中间温区出现磁电阻的温度稳定性。     

(1-x)La0.7Ca0.3MnO3/xAg磁电阻的温度稳定性

用固相反应法将Ag引入La0.7Ca0.3MnO3颗粒表面,形成(1-x)La0.7Ca0.3MnO3/xAg(x=0.00,0.10,0.20,0.25,0.30,0.35)。通过XRD谱、扫描电子显微镜(SEM)照片及SEM能谱(EDS)、ρ-T曲线、ρ-T拟合曲线、MR-T曲线,研究电输运性质及MR温度稳定性。结果表明:随复Ag量增大,电阻率急剧下降,高复Ag(x≥0.3)的电阻率比低复Ag(x≤0.10)的电阻率下降2个数量级;发现x=0.00,0.10用ρ-T2公式拟合比较合理,是单磁子散射作用;x=0.20,0.25用ρ-T2.5公式拟合比较合理,是自旋波散射作用;x=0.30,0.35,分别在97,93 K以上用ρ-T4.5公式拟合比较合理,说明是电子-磁子散射作用;所有复Ag样品,在250～20 K温区MR表现出很好的温度稳性,特别是x=0.10的样品,在220～150 K温区MR保持(13.8±0.2)%。提出磁电阻稳定性的机制:Ag与钙钛矿颗粒形成电输运二元通道,钙钛矿颗粒通道产生的低场磁电阻与Ag通道产生的正常磁电阻共同作用,产生MR温度稳定性。     

非化学计量(La0.6Dy0.1Sr0.3)1-xMnO3的电输运及MR温度稳定性机制研究

用固相反应法制备了非化学计量的(La0.6Dy0.1Sr0.3)1-xMnO3(x=0.00,0.10,0.20,0.30,0.35)系列样品,通过XRD、ρ-T曲线、MR-T曲线,研究电输运及磁电阻(MR)温度稳定性的机制。XRD检测表明,非化学计量的(La0.6Dy0.1Sr0.3)1-xMnO3在1200℃下烧结24 h,实际形成了La0.6Dy0.1Sr0.3MnO3钙钛矿相和Mn2O3相组成的二相复合体材料。电输运性质均表现出绝缘体-金属相变,ρ-T曲线高温区出现尖峰,较低温区出现"肩峰",是钙钛矿体相内双交换作用和晶界处电子自旋极化隧穿引起的电阻率共同作用的结果。MR-T表现出,在高温区出现磁电阻峰,在低温区随温度降低磁电阻持续增大,表现出低场磁电阻特征,在中间温区出现磁电阻的温度稳定性,用La0.6Dy0.1Sr0.3MnO3钙钛矿颗粒体相产生的本征磁电阻与颗粒界面效应产生的隧穿磁电阻的叠加给出解释。x=0.30的样品,0.8 T磁场下,在258 K～198 K温区,产生的磁电阻为(6.3±0.2)%。     

钙钛矿锰氧化物(La_(0.9)Eu_(0.1))_(4/3)Sr_(5/3)Mn_2O_7的磁性和电输运性的研究

采用传统固相法制备钙钛矿锰氧化物(La_(0.9)Eu_(0.1))_(4/3)Sr_(5/3)Mn_2O_7多晶样品。通过XRD表明,样品(La_(0.9)Eu_(0.1))_(4/3)Sr_(5/3)Mn_2O_7呈现单相性良好;通过对磁化强度随温度变化(M-T)、磁化强度在不同温度下随磁场变化曲线(M-H)和电子自旋共振ESR谱线表明,随着温度的升高,样品先后经历了三维长程铁磁有序转变点(T_C~(3D)≈75 K)和二维短程铁磁有序转变点(T_C~(2D)≈227 K),在T_C~(3D)与T_C~(2D)之间,系统处于铁磁与顺磁混合态;当温度达到360 K系统进入纯顺磁态,另外样品在低温区(T_C~(3D)以下)出现类团簇自旋玻璃特征。通过磁电阻随温度变化的ρ-T曲线,在T≈84 K附近,样品出现最大磁电阻。而且通过对(La_(0.9)Eu_(0.1))_(4/3)Sr_(5/3)Mn_2O_7的ρ-T曲线拟合,得到样品在高温区域的导电方式为热激活模型。     

La_(0.4)Ca_(0.6)Mn_(1-x)Ga_xO_3体系的电荷有序相

用固相反应法制备La0.4Ca0.6Mn1-xGaxO3(x=0,0.08,0.10,0.12,0.15)系列多晶样品。通过X射线衍射(XRD)图谱、电阻率-温度(ρ-T)曲线、磁化强度-温度(M-T)曲线和电子自旋共振(ESR)图谱,研究Ga3+替代Mn3+对La0.4Ca0.6Mn1-xGaxO3体系电荷有序相的影响。结果表明,当Ga掺杂量高达15%时电荷有序相仍然没有被破坏。这是因为Ga3+是非磁性离子,而La0.4Ca0.6MnO3是CE型反铁磁电荷有序相结构,Ga3+替代Mn3+只是仅仅起到把体系中的长程自旋序破坏为短程自旋序的作用,同时随Ga替代量增大,Mn3+与Mn4+的比远离双交换的最佳摩尔配比(Mn3+∶Mn4+=2∶1),不利于双交换,因而非磁性的Ga3+替代Mn3+难以破坏La0.4Ca0.6MnO3的电荷有序相。     

钙钛矿氧化物La0.3Ca0.7MnO3的磁性质

采用固相反应法制备了样品La0.3Ca0.7MnO3. 通过测量样品的M-T曲线、 M-H曲线和ESR曲线, 研究了La0.3Ca0.7MnO3的磁性质. 结果表明 在262 K时形成电荷有序相(CO相). 当T＞262 K时, 表现为顺磁;当T＜190 K时, 表现为长程反铁磁(在AFM本底中存在少量FM成分);从262～190 K(TCO), 随温度降低在电荷有序态下从顺磁向反铁磁转变.     

Superconducting Transition Temperature in YBa2Cu4O8/La2/3 Ca1/3 MnO3 / YBa2 Cu4O8 Heterostructure

YBa2Cu4O8/La2/3 Ca1/3 MnO3/YBa2Cu4O8 （ Y-124/LCMO/Y- 124） heterostructure was prepared by facing-target sputtering technique. The oscillatory superconducting transition temperature was observed when the thickness of LCMO d L is larger than critical thickness d L^CR. The metal-insulator transition temperature can only be detected at d L 〉 d L^CR. The dependence on the spacer layer in LCMO/Y-124 systems suggests strongly the interplay of ferromagnetic and superconducting couplings.     

CaO--TiO2--Fe2O3三元系中Ca3TiFe2O8的生成机理

钒钛磁铁矿是烧结矿重要的原料之一,Ca₃TiFe₂O₈作为钒钛烧结矿中矿物被发现之后,其生成机理尚不明确.本文采用X射线衍射分析、元素能谱分析和TG-DSC分析相结合的方法,研究了Ca₃TiFe₂O₈的生成机理以及不同温度、CaO与TiO₂含量下Ca₃TiFe₂O₈的生成规律.实验结果表明,Ca₃TiFe₂O₈由Ca₂ Fe₂O₅和CaTiO₃反应生成,即CaO和Fe₂O₃反应生成Ca₂ Fe₂O₅;其后,与CaTiO₃反应生成Ca₃TiFe₂O₈.反应时间越长,Ca₃TiFe₂O₈的生成量越大,但反应温度对Ca₃TiFe₂O₈生成的影响并不明显.另外,还发现CaO含量越高,Ca₃TiFe₂O₈越易于生成,而且等摩尔Fe₂O₃和CaO下只要存在TiO₂,就会有Ca₃TiFe₂O₈生成.      

Effect of Fe2O3 Loading Amount on Catalytic Properties of Monolithic Fe2O3/Ce0.67Zr0.33O2 -Al2O3 Catalyst for Methane Combustion

Ce0.67Zr0.33O2-Al2O3 solid solution was prepared by the co-precipitation method. Fe2O3-based catalysts supported on the solid solution were obtained by the impregnation method. The article revealed that the optimal loading amount of Fe2O3 on Ce0.67Zr0.33 O2-Al2O3 in our experimental condition for catalytic combustion of methane was 8% （ mass fraction）. The prepared catalysts were characterized by BET, TPR, XRD analyses, and their catalytic activity was investigated after being calcined at 873 K and after being aged in water gas at 1273 K. When the loading amount of Fe203 was 8% （ mass fraction）, the catalyst held the highest activity, and the best temperature speciality and thermal stability. The complete-conversion temperature of methane for fresh and aged sample was 788 and 838 K, respectively. The range between the light-off temperature and the complete-conversion temperature was only 15 K. The characterization results of XRD indicated that Fe2O3 was well dispersed on the Ce0.67Zr0.33O2-Al2O3 matrix. The results of BET and TPR were in good harmony with the catalytic activity results.     

Synthesis and Crystal Structure of A Bimetallic Terbium Complex Tb2 {μ-CH2 SiMe2 NC6 H3 ^iPr2 -2, 6}3 （THF）3

The reaction of 2, 6-^iPr2CbH3NHSiMe3 with Tb（CH2SiMe3）3（THF）2 in benzene at room temperature afforded a binuclear terbium complex Tb2 {μ-CH2 SiMe2 NC6 H3 ^iPr2 -2, 6}3（THF）3. X-ray diffraction revealed that Tb atoms were bridged by three methylene units. One Tb atom was six-coordinated by two nitrogen atoms, three methylene carbons, and one THF molecule, while the other Tb atom was six-coordinated by one nitrogen atom, three methylene carbons, and two THF molecules. Both Tb atoms adopted a distorted trigonal prism geometry.     

Study on thermal expansion behavior of Dy2O3 - Al2O3 - SiO2 glass

Employing Dy2O3, Al2O3, and SiO2 as starting materials, several series of Dy2O3-Al2O3-SiO2 sealing glass were prepared. The relationship between their coefficients of thermal expansion and the contents of Dy2O3, Al2O3, and SiO2 were studied respectively. Experimental results showed that Dy2O3 and Al2O3 had a positive effect on the coefficient of thermal expansion of glass, whereas, SiO2 had a negative effect. The coefficient of thermal expansion of glass showed an apparent linear relation to the contents of these three raw materials, from which an estimation model was built, to calculate the coefficient of thermal expansion of sealing glass. Relative errors of the calculating results to testing results were no more than 2%, which suggested that the estimation model was reasonable. This study provides a good theory reference for the practical utilizing of this sealing material, through which a proper glass composition for good sealing could be easily found.     

Solubility of carbon in CaO-B2O3 and BaO-B2O3 slags

The solubility of carbon in molten CaO-B₂O₃ and BaO-B₂O₃ slags at high temperatures was measured to understand the dissolution mechanism of carbon into the slags. The B₂O₃-bearing slags, which have a wide range of liquids, at the temperature of interest have been applied to investigate the effect of basicity on the solubility of carbon from the saturation of acidic or basic components. The solubility of carbon, as a function of the composition of slags, shows a minimum value, and it is suggested that carbon dissolves by different mechanisms in the acidic and basic slags, respectively. From the infrared spectra measurements, the wave number indicating the B-C bond was found to be about 1150 cm⁻¹ in the acidic region of slags; hence, the incorporation of carbon into the borate network was confirmed qualitatively. The carbide capacity was compared to the nitride capacity, showing that the dissolutions of carbon and nitrogen into the slags are similar.     

Catalytic Partial Oxidation of Methane over Ni/CeO2-ZrO2-Al2O3

Nickel catalysts supported on CeO2-ZrO2-CeO2,ZrO2-Al2O3 and Al2O3 were prepared and characterized by means of X-ray diffraction（XRD）,BET areas,H2 temperature-programmed reduction（H2-TPR）,and X-ray photoelectron spectroscopy（XPS）.Through the test of catalytic partial oxidation of methane（CPOM）,Ni/CeO2-ZrO2-Al2O3 displayed the highest activity,which resulted from its largest BET area and best NiO dispersion.Furthermore,Ni/CeO2-ZrO2-Al2O3 maintained a long-time stability in CPOM,which was attributed to its best coking resistance among all the prepared catalysts.     

Research on Y2O3：Eu Phosphor Coated with In2O3

Y2O3：Eu red phosphor for FED application was prepared by high temperature solid-state reaction. The In2O3 coating by precipitation method to the phosphor was applied and the analyses of XRD, Zeta potential, SEM, EDS and low voltage cathodoluminescence （CL） were conducted for investigating the coating effect. The results showed that In2O3 coating promoted the low voltage CL of the phosphor efficiently. The promotion was possibly due to the enhancement of the surface conductivity of the phosphor grains.     

CaO含量对CaF2-Al2O3-CaO-Ce2O3渣系中Ce2O3行为的影响

在Fe-Cr-Al合金中添加微量的稀土元素可显著改善合金的使用性能, 文中以电渣重熔生产Fe-Cr-Al合金所用稀土渣为研究对象, 根据离子-分子共存理论(IMCT)建立了1 823 K时CaF₂-Al₂O₃-CaO-Ce₂O₃四元渣系热力学质量作用浓度模型.结果表明:当渣系中CaO和Al₂O₃的质量百分数之比维持在1:1, 即w_CaO /w_Al2O3=1时, 随着Ce₂O₃含量增加, 渣中铈铝酸盐Ce₂O₃·Al₂O₃质量作用浓度(活度)显著增加, 但炉渣物相种类没有变化.渣系中Ce₂O₃含量分别在10 %, 20 %, 30 %, 40 %时, w_CaO /w_Al2O3值对组元活度的影响各不相同但有共同特征, 表现在处于约1.0~1.8时, CaO活度增加最迅速, Ce₂O₃活度增加, Ce₂O₃·Al₂O₃活度下降, 说明渣中CaO含量增加促进了Ce₂O₃·Al₂O₃分解而导致Ce₂O₃活度增加, 选取渣系进行熔融和X射线衍射实验, 用jade 5.0软件分析物相, 实验结果与计算一致.      

Visible luminescence of lanthanide ions in Ca3Sc2Si3O12 and Ca3Y2Si3O12

The crystalline materials Ca₃Sc₂Si₃O₁₂ and Ca₃Y₂Si₃O₁₂ were characterized by different crystal structures, as the former is a cubic garnet, while the latter is an orthorhombic compound. We investigated the optical spectroscopy of these materials doped with several trivalent lanthanide ions and compared the results for the two hosts. Polycrystalline samples were prepared by solid state reaction, both undoped and doped with the trivalent lanthanide ions Eu³⁺, Tb³⁺ and Sm³⁺. Emission, excitation and Raman spectra of these materials were measured at temperatures ranging from 300 to 10 K. The optical spectra were assigned and discussed, and the effects of the crystal structure of the host on the spectroscopic behaviour were addressed. The technological potential of these compounds in the field of optical materials and devices was discussed.