Synthesis, and measurement of structural and magnetic properties, of La1-xNaxFeO3(0.0≤x≤0.3) perovskite oxides

Polycrystalline La_1-xNa_xFeO₃ (0.0≤x≤0.3) solid solutions were synthesized by a solution combustion method using glycine as a fuel. The combustion synthesized compounds were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), diffused reflectance (DR) in the UV-vis, and magnetic measurements. The crystal structure examined by X-ray powder diffraction indicated that the samples were single phase and crystallized in an orthorhombic (space group, Pbnm no.62) structure. The parent and sodium-substituted compounds showed canted anti-ferromagnetic behavior associated with an increase in magnetic moment as Na content increased. The changes in magnetic properties of the materials were correlated to the changes in structural features, as shown by Rietveld structural refinement of the materials.     

Ce_xTi_(1-x)O_2 Mixed Oxides Supported CuO Catalyst for NO Reduction by CO

Uptodate ,numerousstudieshaveshownthatrareearthoxidesaretheexcellentstructuralandelec tronicpromoterstoimprovetheactivity ,selectivityandthermalstabilityofcatalysts[1,2 ] .Themostwidelyappliedrareearthoxideinindustrialcatalysisiscer tainlyCeO2 .However ,amajordrawbackofCeO2 isthelossofoxygenstoragecapability (OSC)duetoitssinteringathighertemperature (>75 0℃ ) ,whichleadstothedeactivationofthecatalyst[3 ,4] .Oneap proachpreviouslyusedtostabilizeceriaagainstsinter ingwastodopeitwithotheranti…     

Magnetic and magnetotransport behavior of overdoped nanocrystalline Nd_(1-x)Sr_xMnO_3 (0.50≤x≤0.63)

The nanocrystalline samples of Nd1-xSrxMnO3 (NSMO) (x=0.5, 0.55, 0.60, 0.63) were synthesized by sol-gel based polymeric pre-cursor route. Structural, magnetic and magnetotransport properties were studied systematically. It was found that in the composition range (x=0.50-0.63), Nd1-xSrxMnO3 showed paramagnetic to ferromagnetic (PM-FM) transition in the vicinity of TC～270 K but the FM phase was weakened as the Sr concentration increased. The appearance of weak ferromagnetism was explained in terms of the cor...     

Sr2.7Eu0.2P2-x VxO8(0≤x≤2)的光致发光性质

用溶胶-凝胶方法制备Sr2.7 Eu0.2 P2-x Vx O8(0≤x≤2)样品.采用X射线衍射(XRD)和光致发光谱(PL)来表征样品的晶体结构和发光性能.XRD结果表明:随着x的增大,晶体结构由Sr3 P2 O8相过渡到Sr3 V2 O8相.PL光谱结果表明:适量的P5+掺杂使得Sr2.7 Eu0.2 P2-x Vx O8的发光增强,激发VO43-比直接激发Eu3+更有利于Sr2.7 Eu0.2 P2-x Vx O8的发光.     

溶胶-凝胶法制备(La_(1-x)Sr_x)_2Ce_2O_(7-x)及热物理性能研究

采用溶胶-凝胶法合成(La1-xSrx)2Ce2O7-x系列组分样品.研究结果表明:当Sr的掺杂量(x)小于10%时,(La1-xSrx)2Ce2O7-x系列组分样品都是缺陷萤石结构.随着温度的升高,样品的热膨胀系数(TEC)增大,而热导率(TC)呈减小趋势.在一定温度下,(La1-xSrx)2Ce2O7-x的TEC随x的增大而增大;当Sr掺杂量x在0~7.5%之间增加时,样品的热导率不断减小,至x=7.5%时达到极小值,然后随x的增大,样品的TC又明显增大.     

Emission-tunable Ba2Y1–xScxNbO6:Bi3+ (0 ≤ x ≤ 1.0) phosphors for white LEDs

Here, we report a series of Bi³⁺-doped Ba₂Y_1–xSc_xNbO₆ (0 ≤ x ≤ 1.0 mol) phosphors by using the traditional high temperature solid-state reaction. To achieve the structural and photoluminescent (PL) information, several experimental characterizations and theoretical calculations were carried out, including X-ray diffraction (XRD), Rietveld refinement, UV-visible diffuse reflectance and PL spectra, temperature dependent PL spectra, and density functional theoretical (DFT) calculations. The XRD results show that the Bi³⁺-doped Ba₂Y_1–xSc_xNbO₆ samples belong to the double-perovskite phase with a cubic space group of Fm3?m, and the diffraction positions shift toward high diffraction angle when the larger Y³⁺ ions are gradually replaced by the smaller Sc³⁺ ions. In addition, the refined XRD findings show that the Bi³⁺ ions tend to substitute the Y³⁺ and Sc³⁺ sites in the Bi³⁺-doped Ba₂Y_1–xSc_xNbO₆ (0 < x < 1.0 mol) solid solutions. The PL spectra show that the emission positions of the solid solution samples tune from 446 to 497 nm with the increase of Sc³⁺ content, which can be attributed to the modification of crystal field strength around Bi³⁺ ions. Moreover, there is energy transfer from the Ba₂YNbO₆ host to Bi³⁺ ions, which is dominated by a resonant type via a dipole-quadrupole (d-q) interaction. The Ba₂Y_0.6Sc_0.4NbO₆:0.02 molBi³⁺ shows the strongest PL intensity under 365 nm excitation, with the best quantum efficiency (QE) of 68%, and it keeps 60% of the room temperature emission intensity when the temperature increases to 150 °C, meaning that the Ba₂Y_0.6Sc_0.4NbO₆:Bi³⁺ features excellent thermal quenching of luminescence. By combining this optimal sample with a commercial red-emitting Sr₂Si₅N₈:Eu²⁺ phosphor, and a commercial 365 nm UV LED chip, a white LED device, with the color temperature (CT) of 3678 K, color rendering index (CRI) of 67.9, and CIE coordinates at (0.371, 0.376), is achieved.     

钙钛矿化合物SrFe_(1-x)Cu_xO_(3-δ)(0≤x≤0.3)的制备及磁性

采用溶胶-凝胶法制备钙钛矿结构化合物Sr Fe1-xCuxO3-δ(0≤x≤0.3)的多晶样品,通过X射线衍射(XRD)结合Rietveld结构精修方法研究该化合物的晶体结构,并使用物性综合测量系统(PPMS)研究其磁性能。精修结果表明掺Cu可使样品发生结构转变,x=0的样品为I4/mmm点群的正方结构,而x=0.1,0.2,0.3的样品均为Pm 3 m点群的立方结构,晶格常数随Cu含量的增加而减小。磁性测量的结果表明Cu含量越高,造成铁磁和反铁磁相互作用的竞争越激烈,形成自旋玻璃态;x=0.1,0.2,0.3的样品转变温度低于x=0的样品,但随Cu含量增加,x=0.1,0.2,0.3的样品转变温度逐渐升高;随Cu含量增加,Fe/Cu位的有效磁矩减小。     

溶胶凝胶法制备超细Li_(2 x)Sm_xSi_(1-x)O_3及其离子导电性研究

以无机盐和金属醇盐为前驱物 ,用溶胶 凝胶法制备了超细Li2 xSmxSi1-xO3(x =0～ 0 0 9) ,用DTA、XRD、TEM及交流阻抗等技术对样品的结构、形貌、粒径及离子导电性等进行了观察和测试。其固溶体形成范围是 0 相似文献   

YBa_2Cu_3O_(7-x)-Nb_2O_5系超导体制备及结构

日本研究人员在950℃恒温24h,制成了掺Nb_2O_5的 YBa_2Cu_3O_(7-x)超导体,其冷却速率为5℃/min。在 Nb_2O_5≤0.5wt%范围内,当增加Nb_2O_5掺杂量时,超导体体密度及临界电流密度(77K,H=0T)分别增至5.80g/cm~3和437     

钙钛矿锰氧化物Nd_(1.2-x)Tb_xSr_(1.8)Mn_2O_7(x=0,0.10,0.15)的类Griffiths相研究

采用固相反应法制备了Nd_(1.2-x)Tb_xSr_(1.8)Mn_2O_7(x=0,0.10,0.15)系列多晶样品,通过样品的XRD谱线,磁化强度随温度、外加磁场的变化曲线(M-T、M-H)等研究样品的晶体结构和磁性。研究结果表明,随掺杂量的增加,样品的结构没有发生明显变化,均为单相的Sr_3Ti_2O_7型四方结构,空间群为I4/mmm。在测量温度范围内,随温度的降低,三个样品分别先后经历了顺磁态、铁磁-顺磁共存态和反铁磁-铁磁共存态的转变。三样品体系中均存在类Griffiths相,在类Griffiths相温度(T_G≈275 K)以上,样品处于顺磁态;在类Griffiths相温区(θT275 K,其中θ为居里温度)范围内,样品处于铁磁-顺磁共存态;在奈尔温度(T_N)以下,样品铁磁性减弱,反铁磁性增强,铁磁和反铁磁性相互竞争导致类自旋玻璃行为出现。此外Tb元素的掺杂对系统中类Griffiths相温度基本没有影响,但对类Griffiths相温区有一定影响。     

低碳钢中第2相NbC_xN_(1-x)的x值

采用现有计算方法,对低碳钢中铌的碳氮化物NbCxN1-x中的x值进行了理论计算.计算结果表明,NbCxN1-x中的x值主要受成分和温度的影响,随钢中C含量增大、N含量减小而增大,随温度的升高而减小之.通过与相关实验结果比较发现:在一定的成分、温度范围内计算结果与之符合良好;对于超出该范围的Nb微合金化低碳钢,计算结果可作参考.给出了温度和范围成分分别为1050～1250℃和0.10%C-0.005%N-0.20%Nb～0.20%C-0.005%N-0.20%Nb.     

Y_(1—x)Ag_xBa_2Cu_3O_(7—y)的结构及超导电性

研究了Y_(1-x)Ag_xBa_2Cu_3O_(7-y)体系的结构。当x≤0.15时.该体系是固溶体.当0.150.5时,体系失去超导电性。在固溶体范围,Ag的置换改善了纯的YBCO脆性,增加了材料的机械强度,改善了颗粒弱连接.使体系的Jc从94.6A/cm~2提高到362A/cm~2。     

Magnetic and electric characteristics and abnormality of low-temperature resistivity in La0.67-xErxSr0.33MnO3(0.00≤x≤0.20) system

M-T curves, p-T curves, and MR-T curves of La0.67-xErxSr0.33MnO3 (x=0.00, 0.10, 0.20) system were studied by experiments. The experiments showed that: with increasing the doping amount, the magnetic structure of the system transformed from long-range ferromag-netic ordering to spin-cluster glass state, and M-T curves bent up in the extremely low temperature range; the resistivity of the system in-creased with increasing doping amount and exhibited the minimum phenomenon of low-temperature resistivity. The variation of the mag-netic and electric properties came from the extra magnetic coupling induced by the doping and from the Kondo effect induced by the lattice distortion and local magnetic moments which was similar to that induced by the mattering of magnetic impurities on electron spins.     

磁控溅射法制备YBa_2Cu_3O_(7-x)双面超导薄膜

采用大直径中空柱状阴极磁控溅射装置和筒形加热器制备了高质量YBa2 Cu3O7-x双面超导薄膜。使用衬底为 (0 0 1)LaAlO3和 (0 0 1)YSZ。双面超导薄膜零电阻温度TC=89～ 91K ,临界电流密度JC≥ 10 6A/cm2 (77K ,零场下 ) ,微波表面电阻RS<1mΩ(77K ,10GHz)。对不同氧氩比下制备的双面膜进行了性能的比较。当O2 ∶Ar =1∶2 .5 ,衬底温度在80 0℃时 ,制备出了高质量的双面超导薄膜。同时对双面超导薄膜进行了微结构分析。用制备的 2 5mm× 2 0mm双面膜研制成功中频滤波器 ,中心频率为 1 0 6GHz时 ,插损为 0 6 7dB。     

稀土超导材料YBa_2Cu_3O_(7-x)相结构分析

用Y_2O_3,CuO,BaCO_3粉末烧结制得了超导材料,并对该材料的微观结构进行了X射线衍射及透射电镜分折,确认在超导相晶体内存在有规则排列的氧空位。     

Characterization of (Y,Gd)B_xV_(1-x)O_(4-x)∶Eu Phosphor Prepared by Coprecipitation Reaction

The PDP have been widely used for large flatpanel displays.Phosphors for the application in PDPare required to have high conversion efficiency by theVUVradiation of147and/or172nmfromthe Xe andXe-He gas plasma[1].In order to have a good picturequality,much attention has been paid to i mprove ordevelop novel PDP phosphors[2~6].The commercialred emitting PDP phosphor(Y,Gd)BO3∶Eu3+showsthree sharp emissions peaked at593,612and627nm,which are corresponding to the transitions of5D0→7F1,5…     

模板法制备La_2O_3-Ce_xZr_(1-x)O_2催化酯交换反应的研究

以松木屑为模版,制备了La_2O_3-Ce_xZr_(1-x)O_2复合氧化物,用于催化餐饮废弃油合成生物柴油的酯交换反应。采用BET比表面积分析仪、扫描电子显微镜(SEM)对La_2O_3-Ce_xZr_(1-x)O_2进行表征。研究不同制备方法对催化剂活性的影响,分析不同的反应条件对酯交换反应产率的影响。结果表明:当反应条件为x=0.5,催化剂量为餐饮废油质量的5%,甲醇与餐饮废油物质的量的比为54∶1时,在165℃下反应4.5h左右,酯交换反应获得生物柴油的产率为91.1%。     

Catalysis of Ce_xZr_(1–x)O_2 for di-iso-propyl-ether hydration

The catalytic potential of CexZr1–xO2 in isopropyl ether(DIPE) hydration was explored. While the acidic H-zeolite catalyst was favorable for propylene formation through carbenium ion mechanism, Ce-ZSM-5 and CexZr1–xO2 catalysts improved product selectivity of isopropyl alcohol(IPA) through redox mechanism. The catalytic property of CexZr1–xO2 depended on the preparation method and variable, type of cerium precursor and Ce/Zr ratio. By means of characterizations with X-ray diffraction, N2 adsorption isotherms and NH3 temperature programmed desorption, tetragonal phase of CexZr1–xO2 was proposed as the active phase in which CeO2 and ZrO2 catalyzed synergistically the DIPE hydration with IPA product selectivity. The CexZr1–xO2 prepared from cerium sulfate precursor with co-precipitation hydrothermal method exhibited maximum catalytic activity and IPA product selectivity. The precursor effect was attributed to the stabilization of SO42– species on the tetragonal phase of CexZr1–xO2 and super solid acidity.     

Thermal and transport properties of La_(2–x)Nd_xMo_2O_9

Single-phase La_(2–x)Nd_xMo_2O_9(0≤x≤1.8) compounds were prepared using solid-state reaction technique. Their structural and thermal p roperties were characterized by room and high temperatures X-ray diffraction(XRD), thermo gravimetric analysis-differential scanningcalorimetry(TG-DSC), and high temperature Raman spectra. The transport properties were investigated using D.C. four-probe technique and Hebb-Wagner polarization method. The substitution limit of Nb~(3+) in La_(2–x)Nd_xMo_2O_9 was determined to be in the range of 1.8x1.9, and the cubic lattice parameter of La_(2–x)Nd_xMo_2O_9 decreased linearly with the increasing of x. When the Nb~(3+) substitution content x was larger than 0.6, the α/β phase transition could be depressed to such a great degree that the phase transition thermal enthalpy was not detected by DSC. The temperature dependence of electrical conductivities for La_(1.4)Nd_xMo_2O_9 below 873 K and that for LaNdMo_2O_9 below 923 K obeyed the Arrhenius law, while above 873 and 923 K Vogel-Tammann-Fulcher(VTF) model could describe the conduction behaviors satisfactorily. The transition of transport mechanism from Arrhenius to VTF was caused by the change of structure, which was supported by the high temperature XRD and Raman results. The ionic transport number of La_(1.4)Nd_xMo_2O_9 in air was larger than 0.99 at 1073 K, and with the increasing of temperature it was close to 0.98 at 1173 K. In view of the phase transition, thermal expansion and conductivity properties, La_(1.4)Nd_xMo_2O_9 should be a promising electrolyte material in La_(2–x)Nd_xMo_2O_9 series.