锰位Cu离子掺杂对层状锰氧化物La1.2Ca1.8Mn2O7电磁性能的影响

研究了Cu离子掺杂对层状钙钛矿结构锰氧化物La1.2Ca1.8Mn2O7电磁性能的影响.观察到低含量Cu掺杂样品铁磁性减弱,出现金属-绝缘转变与团簇玻璃态行为;高含量Cu掺杂样品为绝缘体,出现顺磁与自旋玻璃态行为.相对小极化子跃迁模型或热激活半导体带隙模型而言,可变程跃迁模型更好地描述了载流子在顺磁状态的电输运机制.     

Structural Characterization and Magneto Electrical Behavior of Sm Doped La0.7Ca0.3MnO3 Manganites

The La_0.7?x Sm _x Ca_0.3MnO₃ with x=0.0 and 0.1 compounds were fabricated by compositional solid state reaction method and investigated for their structural and magnetoelectrical properties. The samples are characterized structurally by X-ray diffraction, scanning electron microscope, and energy dispersive X-ray spectrometer. The electrical and magnetotransport properties of bulk samples have been investigated in the temperature range 5–300 K and a magnetic field up to 7 T. The metal–insulator transition temperature, T _MI, decreased with samarium (Sm) doping and also it is increased slightly with the application of magnetic field. The results of Sm doped LCMO compound showed that the maximum magneto resistance (MR) is about 54 % and it appears near the transition temperature.     

Low-Temperature Neutron Diffraction and Magnetic Properties of La1.2Sr0.9Ca0.9Mn2O7

The crystal structure and magnetic properties of a typical polycrystalline double-layered manganite, La_1.2Sr_0.9Ca_0.9Mn₂O₇, were examined using neutron diffraction and magnetization techniques. Neutron diffraction was performed at low and room temperatures and the crystal structure was refined using the Rietveld method based on the space group I4/Mmm. Low temperature neutron diffraction and magnetization measurements clearly revealed antiferromagnetic ordering. A neel transition was observed at approximately 150 K.     

Thermoelectric Properties of the Layered Compound GeBi4Te7 Doped with Copper

The effect of Cu doping (0.05–0.20 at. %) on the thermoelectric and transport properties of the layered compound GeBi₄Te₇ (with a small Ge deficiency) was studied. According to x-ray diffraction data obtained on cleaved (001) surfaces, Cu doping increases the c cell parameter, presumably because some of the Cu atoms are incorporated in the van der Waals gaps between the five- and seven-layer slabs. In addition, Cu doping reduces lattice thermal conductivity and increases electron mobility. The thermoelectric figure of merit of the material with the optimum Cu content (0.05 at. %) is ZT = 0.65 around 330 K.     

Synthesis,Structure and Magnetic Properties of Layered Perovskite Sm1.5SrBa0.5Mn2O7

The layered perovskite oxide Sm_1.5SrBa_0.5Mn₂O₇ was synthesized by the conventional method of co-precipitation. Its structure has been solved by powder X-ray diffraction. The diffraction patterns are consistent with the I4/mmm symmetry, with tetragonal lattice parameters a=3.8398(7) Å and c=20.3814(5) Å. The structure of Sm_1.5SrBa_0.5Mn₂O₇ is similar to Sr₃Ti₂O₇. Magnetic measurements were also performed in the temperature range 2–360 K. They showed a strong presence of antiferromagnetic interactions below Neel temperature T _N=25 K. The variation of the magnetization with the magnetic field in a temperature of 5 K was also analyzed. No saturation was observed up to the high applied magnetic field of 10 T.     

Magneto-Transport Properties of the Rutheno-Cuprate RuSr2GdCu2O8

RuSr ₂ GdCu ₂ O ₈ (Ru-1212) is a triple perovskite containing both CuO ₂ and RuO ₂ layers. It has attracted a great deal of interest recently because it displays electronic ferromagnetism and superconductivity coexisting on a microscopic scale, with T _Curie 135K and T _c up to 50K. ^{1, 2} We report magnetisation and magnetoresistance (MR) data that exhibit effects due to the interaction between the ferromagnetic ruthenium moments and the conduction electrons. The MR is negative at temperatures above T _Curie , and is proportional to the square of the applied field well above this temperature. Below T _Curie the MR displays a positive peak at fields of around 15 kOe, but at high fields it becomes negative again, and approximately linear. We analyse the high temperature data in terms of spin-disorder scattering theory and extract a value for the exchange interaction between the carriers in the CuO ₂ planes and the Ru spins.     

The Effect of Mn Substitution on Properties of Bi1.6Pb0.4Sr2Ca2?x Mn x Cu3O y Superconductors

The effects of Mn substitution on the physical properties and structural characteristics of Bi_1.6Pb_0.4Sr₂Ca₂Cu_3−x Mn _x Oy (Bi-2223) superconductor system have been studied. For this, the samples of nominal composition Bi_1.6Pb_0.4Sr₂Ca₂Cu_3−x Mn _x Oy (x=0.00, 0.10, 0.15 & 0.20) was prepared by the solid-state reaction method. It has been found that the effects of Mn substitution favor the formation of Bi-2223 phases. The phase identification/gross structural characteristics of synthesized (HTSC) materials explored through powder X-ray diffractometer reveals that all the samples crystallize in orthorhombic structure with lattice parameters (a=5.4918 ?, b=5.4071 ?, and c=37.0608 ?) up to Mn concentration of x=0.20. The critical transition temperature (T _c) measured by standard four probe method has been found to depress from 108 K to 70 K and transport current density (J _c) has been increased from 4.67×10² to 3.52×10³ A cm⁻² as Mn content (x) increases from 0.00 to 0.20. The surface morphology investigated through scanning electron microscope and atomic force microscopy (SEM and AFM) results that voids and grains size increases as the Mn concentration increases besides the nanosphere like structures on the surface of the Mn doped Bi-2223 sample.     

Effect of Heat Treatments and Zr Doped on Superconducting Properties of Bi1.6Pb0.4Sr2Ca2Cu3O ?? Ceramics

The effects of heat treatments and the role of Zr have been studied using X-ray diffraction (XRD) method and resistance measurement technique equipment for the structural identification and determination of critical temperature, T _C. Generally, all samples displayed a normal metallic behavior above T _Conset. The values of T _C(R=0) have been found to decrease as Zr concentration increases. Heat treatments at 830 and 860???C; however, have increased the critical temperature, T _C in samples x=0.15 and x=0.20. The volume of the 2223-phase ratio on 2212-phase has decreased gradually toward Zr concentration. However, for samples x=0.15 and x=0.20, the ratio of 2223-phase was improved after applying heat treatment processes. The crystallographic structure remains in a tetragonal form where a=b??c. A?few Zr is still existed in sample x=0.15 and x=0.20 although after sintering and heat treated at 830???C implies that the excess Zr cannot incorporate into the crystalline structure of BSCCO system. After the heat treatment process at 860???C, all these Zr peaks suddenly disappeared, and hence improved the volume of 2223-phase.     

A Study of Structural and Physical Properties of Heavily Co-doped LaSr2Mn2O7 Bi-layered Manganite

In this paper, we report the influence of cobalt doping on the structure and magnetic properties of bilayered-perovskite LaSr₂Mn_2?x Co _x O₇ (x=0.25,0.3). Parent and doped samples were synthesized through the sol-gel method under optimized conditions. X-ray diffraction studies coupled with the Rietveld refinement of xrd data, show that both doped and parent samples crystallize in a Sr₃Ti₂O₇-type layered perovskite structure. Temperature dependent magnetic behavior of the parent sample exhibits an antiferromagnetic and a charge-ordering state around 220 K. Magnetic field dependence of magnetization M(H) for doped samples at 20 K show well-defined M–H loops confirming the formation of intrinsic ferromagnetic ordering due to the Co doping. Additionally, we studied the ac–magnetic susceptibility and magnetization relaxation process in our samples. Dynamic scaling analysis hints an existence of glassy magnetic states in doped samples. Electrical and magnetic properties of our samples further demonstrate that Co doping suppresses charge ordering in bilayered LaSr₂Mn₂O₇.     

纳米La2Ti2O7粉末的低温水热合成及光催化性能的研究

采用水热反应法,在180℃的低温下制备出纳米La2Ti2O7粉末,并对产物进行了X射线衍射、扫描电镜、透射电镜、比表面积和紫外可见光谱的表征测试.用紫外光照射甲基橙溶液的光催化降解实验研究了制备样品的光催化活性,并比较了不同制备温度对其降解甲基橙效率的影响.     

添加剂对La2Ti2O7陶瓷性能的影响

研究了ZnO,Nb2O5和H3BO3的加入对La2Ti2O7陶瓷的烧结和介电性能的影响,并对影响机理作了初步探讨.结果表明选择合适种类和数量的添加剂能够使La2Ti2O7陶瓷在1220～1300℃之间烧结.添加1%(质量分数,下同)ZnO,0.5%Nb2O5和3%的H3BO3的La2Ti2O7陶瓷的介电常数分别为48和40,介电损耗在10-4数量级;在10kHz下,介电常数的温度系数分别为-24×10-6/℃和-48×10-6/℃,是一种性能良好的介质材料.     

Structural, magnetic, and electron transport studies on nanocrystalline layered manganite La1.2Ba1,8Mn2O7 system

The structure property relationship for Ru doped La1.2Ba1.8Mn2-RuxO7 system has been studied systematically. The system crystallizes in the single-phase tetragonal structure with space group of 14/mmm. The unit cell volume is found to increase with Ru doping. The sheet type microstructure could be seen in this system, which is important for anisotropic nature of layered structure. The crystallite size is found to be 25 nm indicating nanocrystalline nature of the system. Ferromagnetic to paramagnetic (Tc) transition above the room temperature is observed in all except the highest doped Ru (x = 1.0) where the Tc is 254 K using a.c. susceptibility measurement. The large values of magnetoresistance for the x = 0.0 sample at 10 K is found to be 57% and 64% at applied fields of 5 and 10 T, respectively.     

Ce掺杂Sr2MgSi2O7的溶胶-凝胶法制备及性能研究

采用溶胶－凝胶（sol-gel）法制备稀土离子Ce掺杂的Sr2MgSi2O7硅酸盐基发光材料,通过X射线衍射仪（XRD）、透射电子显微镜（TEM）、荧光分光光度计（PL）对样品的晶体结构、形貌及光学性能进行测试。XRD测试结果表明,在较低的热处理温度下可获得Sr2MgSi2O7相,但样品中也存在少量的其它杂质相。荧光光谱测试结果表明,经1000℃氢气处理1％Ce离子掺杂Sr2MgSi2O7样品中存在两套不同的光致发光带,一个为321nm光激发产生的371nm紫外发光,另一个为350nm激发产生的400—450hm的宽带可见发光,通过分析表明两个发光带分别起源于不同基体中的Ce^3＋离子。     

DSC study on the phase transition of BaSm2Mn2O7 and BaEu2Mn2O7

The phase transition of BaSm₂Mn₂0₇ and BaEu₂Mn₂O₇ were studied by differential scanning calorimetry (DSC). Transition temperatures and enthalpy changes accompanying the phase transition for stoichiometric BaSm₂Mn₂O₇ and BaEu₂Mn₂0₇ were measured. The transition temperatures, 525K and 550K for BaSm₂Mn₂O₇ and BaEu₂Mn₂O₇, respectively, determined in this study, are in good agreement with the previous results of high temperature X-ray diffractometry. The enthalpy changes of the transition between orthorhombic and tetragonal structures, ΔH_tr^O, were 0.6 kJ/mol and 1.9 kJ/mol for BaSm₂Mn₂O₇ and BaEu₂Mn₂O₇, respectively.     

La掺杂AgSnO2触头材料的电性能

由于Cd有毒性,AgSnO2触头材料逐渐取代了 AgCdO 成为新型触头材料,但由于AgSnO2触头材料中的SnO2近乎绝缘,使得触头材料的接触电阻增大,故改善SnO2的导电性是急需解决的重大难题.本文提出了一种简单的、低成本的La掺杂AgSnO2触头材料的设计方法.采用模拟计算的方法,利用第一性原理的密度泛函理论平面波超软赝势法,建立了SnO2以及不同比例La掺杂的SnO2超晶胞模型,在对其进行几何优化之后分别研究了 La掺杂比为50%、25%、16. 67%、12. 5%、8.34% 的SnO2材料的电子结构,并研究了其晶格参数、能带结构和态密度等.结果表明,掺杂后材料晶胞体积变大. La的5d轨道进入导带,使得导带底向低能端移动,禁带宽度变小.最终得出La掺杂比为16.67% 时导电性最佳.最后进行了不同掺杂比下触头材料的电接触性能试验,得到了接触电阻和燃弧能量等电接触性能参数并验证了模拟结果.因此,本文的研究为触头材料的发展和应用提供了理论依据.