Electrical Transport and Magnetic Properties of La0.67Ca0.33Mn1-xCrxO3 and La0.67＋xCa0.33-x Mn1-xCrxO3 （0.04≤x≤0.08）

A comparative study for two different series, La0.67Ca0.33Mn1-xCrxO3 and La0.67＋xCa0.33-x Mn1-xCrxO3 is performed with x changing from 0.04 to 0.08 through measurements of zero-field resistivity （p）, magnetoresistance （MR） and ac susceptibility （Z） as functions of temperature （T）. For the second group, a single insulator-metal transition was characterized by the resistivity maximum appears in p vs. T curve. For the first group, besides the resistivity peak appearing at higher temperatures, the sample shows evidence for the existence of another peak appearing at lower temperatures. Compared to the first group, the second group shows a significant enhancement in MR effect, while the measurement ofΧ-T dependence does not display obvious differences for the two series. Different behaviors observed in the two series are discussed by considering possible exchange interaction between Mn^3- ion and Cr^3- ion.     

Enhanced Low-field Magnetoresistence in the Absence of Mn Content in Polycrystalline La0.67Ca0.33MnO3

Magnetic and electrical transport properties of the La0.67Ca0.33Mn1-xO3 （x=0-0.16）, which were prepared by the sol-gel method followed by sintering treatment at 1 450, 1 100 and 900 ℃, respectively, were investigated. Experimental results show that, with the increase of x, the resistivity of samples increases and the insulator-metal transition temperature shifts towards lower temperature. Meanwhile, the intrinsic megnetoresistance effect is weakened and the extrinsic magnetoresistance is enhanced. For the samples with x=0.16 and 0.10 sintered at 1 100 ℃ and 900 ℃, respectively, low field magnetoresistance as high as about 50% can be observed. Furthermore, for the samples sintered at 1 100 ℃ and 900 ℃, the grain size is not only controlled by about sintering temperature, but also by the absence of Mn content x.     

Preparation and Monte Carlo Simulation of La0.67Ca0.33MnO3/Cr2O3 Composites

The （ 1 - x ） La0.67Ca0.33MnO3 （ LCMO ） ＋ x Cr2O3 composites were synthesized by a new liquid phase method. The XRD and SEM meusurements reveal that few Cr2O3 were soluble in the LCMO structure and the lattice constant of LCMO almost did not change, while most Cr2O3 were distributed at the grain boundaries or on surfaces of the LCMO grains. In resistivity versus temperature meusurements, a metal-insalator transition was observed when x 〈 0.20. The resistivity increases and the metal-insalator transition temperature deereases with the increasing content of Cr2O3 . A random resistor network （RRN） model was used to simulate the transport property of the mixture samples. The simulation results agree with the experimental observations. The results show that the method is reasonable for understanding the electronic transport of the composites of the manganite.     

自蔓延高温合成La0.67Sr0.33MnO3-δ粉体的研究

采用自蔓延高温合成(SHS)技术合成了La0．67Sr0．33MnO3-δ粉体。研究了KMnO4含量、压坯密度对燃烧反应及退火温度对粉体性能的影响，并用XRD、SEM对粉体的性能进行了表征，结果表明：KMnO4用量为0．3时，反应完全且晶粒大小均匀；反应的原料混合物压坯密实度的降低可使燃烧温度有所增大；最佳退火温度为1100℃。     

Chemieal Synthesis and Magnetie Properties of Nanocrystalline （La0.67-XGdx）Sr0.33MnO3 Using Amorphous Molecular Alloy as Precursors

A new route to synthesize nanosized crystalline of （La0.67-xGdx）Sr0.33MnO3 （X=0.05, 0.10, 0.15, 0.20） perovskite-type complex oxides at calcination temperature of 600-1000℃ using the amorphous molecular alloy as precursors was reported. The precursor could be completely decomposed into complex oxide at temperature below 500℃ according to the TGA and DTA results. XRD demonstrates that the decomposed species is composed of perovskite-type structure at calcination temperature of 600℃ for 2 h. The particle size that depends on the calcination temperature of the precursor is in a range of 30-120 nm as determined by transmission electron microscopy （TEM）. This method is effective and can be easily quantitatively controlled to synthesize nanosized perovskite-type complex oxides. The magnetic properties of （La0.67 xGdx）Sr0.33MnO3 nanocrystalline were preliminary studied.     

Electrical and Magnetic Properties of Electron Doped BixCa1-xMnO3 （0〈x ≤0.33） Ceramics

Measurements of crystal structures, electrical and magnetic properties for the electron doped BixCa1-xMnO3 （0〈x≤〈0.33） reveal the presence of a variety of notable changes in correlation with magnetic transitions and charge ordering. Samples with x〈0.2 in general show a clear ferromagnetic transitions around 130 K. On the other hand, samples with 0.2≤x≤0.33 show much more complex low-temperature magnetic properties perhaps due to the coupling between the magnetic states and orbital/charge ordering. Structural transformations and structural modulations in the x=0.25 and 0.33 samples have been observed by transmission electron microscopy.     

Transport Properties of Polycrystalline La2/3Ca1/3Mn1-xCuxO3

The infuence of Cu dopant (x) and sintering temperature(Ts) on the troansport propeties of La2/3Ca1/3Mn1-xCuxO3 series samples prepared by Sol-Gel technique was investigated.X-ray diffraction patterns show that all the samples with different Cu dopant and sintering temperatures (Ts) are of single phase without obvious latice distortion.Experimental results indicate that the insulator-metal transition temperature is diectly related to the sintering temperature and Cu dopant x.It is interesting to observe that a proper amount of Cu dompant can substantially improve magnetoresistance effects.     

La0.67Mg0.33Ni2.5Cu0.5贮氢合金磁热处理工艺的正交设计

利用L9（34）正交表安排实验,考察磁热处理的温度、时间及磁感应强度对La0.67Mg0.33N i2.5Cu0.5合金的吸放氢反应热力学和动力学的影响,结合极差分析和方差分析研究了各因素对考核指标的显著性影响,并得到合金磁热处理的优化工艺：热处理温度850℃,处理时间1 h和磁感应强度4 T.在此条件下处理后的合金,吸放氢的质量分数分别为1.33%和1.14%,焓变为-59.69 kJ/mol,吸热峰顶所对应的温度为86.3℃,吸放氢特征时间（tξ=0.875）分别为11.2和108.7 s.结果表明,该合金与其它工艺下的样品相比,吸氢量最大,放氢后物相结构最稳定,吸热峰顶所对应的温度最低,吸放氢速度最快.     

多晶La0.49Sr0.51(Mn1-xNbx)O3的磁电阻研究

采用四探针法测量多晶La0.49Sr0.51(Mn1-xNbx)O3(x=0,0.05,0.15和0.25)在磁场下的电阻率温度曲线.实验结果显示:①在0.45T磁场下,对于x=0和x=0.25的样品,几乎观察不到磁电阻(Magnetoresistance,MR)效应,而对于x=0.05和x=0.15的样品,磁电阻效应较明显.这种差异可能与样品中铁磁相是否占主导作用有关;②比较x=0.05和x=0.15这两种样品的MR机制,前者可能与载流子在弱连接晶界上的自旋相关散射有关,且其主要是非本征的;而后者主要是本征的.     

钙钛矿La0.5Sr0.5Mn1-χCrχO3的制备与磁性研究

采用溶胶-凝胶法制备了La0.5Sr0.5Mn1-χCrχO3(χ＝0.0-0.5)的系列样品,通过XRD,SEM和振动样品磁强计对样品进行表征,结果表明:随掺杂量χ的增加,样品结构从正交向单斜转变,对称性由高向低转变.样品形貌均为球形,颗粒尺寸在0.2-1 μm之间.样品的居里温度随掺杂量χ的增加而降低.     

La1-xZnxMnO3和La2/3Sr_((1-x)/3)Znx/3MnO3的磁电输运特性

用固相反应方法制备La1-xZnxMnO3和La2/3Sr(1-x)/3Znx/3MnO3化合物。La1-xZnxMnO3在不同掺杂浓度x的研究表明:Zn2+在一定浓度范围内掺杂,具有钙钛矿结构,但掺杂浓度在50%~70%时有ZnO衍射峰,其电阻率在100 K以上随温度而下降,当掺杂浓度为x=0.3时电阻率最低。当Zn2+和Sr2+共掺而     

Impedance spectroscopy study on Mn1＋xFe2-2xTixO4 （0≤x≤0.5） ferrites

The complex impedance spectroscopy and surface morphology of Mn_1+x Fe_2−2x Ti _x O₄ (0⩽x⩽0.5) system, prepared using a conventional solid state reaction technique, were investigated. The impedance spectroscopy measurements were carried out at room temperature in the frequency range of 42–5 MHz. The electrical processes in the samples were modeled in the form of an equivalent circuit made up of a combination of two parallel RC circuits attributed to grain and grain boundaries. The DC conductivity obtained by extrapolation of AC data using impedance spectroscopy and four-probe method increases at 10% doping of Ti ions. The energy-dispersive X-ray (EDX) pattern confirmed the homogeneous mixing of the Mn, Fe, Ti and O atoms in pure and doped ferrite samples.     

钙钛矿型La_(0.67)Sr_(0.33)Mn_(1-x)Fe_xO_3的室温磁热效应和磁致伸缩效应

采用溶胶-凝胶工艺制备了La0.67Sr0.33Mn1-xFexO3多晶样品,并研究了其晶体结构、磁热效应及室温下的磁致伸缩效应.其X射线衍射谱表明,所有样品均为钙钛矿结构单相,分析表明,随Fe含量的增加,材料的铁磁居里温度(TC)下降,磁致伸缩系数先增加后降低.     

多晶La0.49 Sr0.51 (Mn1-x Nbx )O3的电输运特性研究

测量了B位掺杂的钙钛矿结构锰氧化物La0．49Sr0．51(Mn1-xNb2)O3(x=0,0.05，0．15和0．25)的电阻率和磁化强度的温度特性．实验结果表明，当Nb^5 部分替代B位的Mn^4 离子时，电阻率-温度特性由原来单一的半导体型转变成了高温时的半导体(绝缘体)型和低温时的类金属型．随Nb掺杂量增大，电阻率迅速升高3～5个数量级，半导体(绝缘体)一类金属转变温度降低．在掺杂Nh的样品中，只观察到顺磁-铁磁转变，而未观察到铁磁一反铁磁转变．上述实验结果的一种可能解释是掺杂改变了磁有序时电子自旋的排列和空间取向，从而改变载流子被自旋热涨落的散射作用和载流子转移的随机性．     

Chemical Synthesis and Magnetic Properties of Nanocrystalline (La_(0.67-X)Gd_X)Sr_(0.33)MnO_3 Using Amorphous Molecular Alloy as Precursors

A new route to synthesize nanosized crystalline of(La 0.67–X Gd X )Sr 0.33 MnO 3 (X=0.05,0.10, 0.15,0.20)perovskite-type complex oxides at calcination temperature of 600-1000°C using the amorphous molecular alloy as precursors was reported.The precursor could be completely decomposed into complex oxide at temperature below 500°C according to the TGA and DTA results.XRD demonstrates that the decomposed species is composed of perovskite-type structure at calcination temperature of 600°C for 2 h.The particle size that depends on the calcination temperature of the precursor is in a range of 30-120 nm as determined by transmission electron microscopy(TEM).This method is effective and can be easily quantitatively controlled to synthesize nanosized perovskite-type complex oxides.The magnetic properties of(La 0.67–X Gd X )Sr 0.33 MnO 3 nanocrystalline were preliminary studied.     

纳米复合氧化物催化剂La0．6Sr0．4Mn1-xCuxO3制备及催化性能

利用柠檬酸络合溶胶-凝胶法制备了由稀土与过渡金属为活性组分的系列纳米复合氧化物催化剂La0.6Sr0.4Mn1-xCuxO3(x=0.0～1.0),通过XRD,TEM,SEM和BET技术考察了以Cu部分取代Mn后的系列催化剂晶体结构、颗粒细度、表面形态和比表面积的变化,并通过对CO的催化氧化反应考察了催化剂的催化活性.结果表明,柠檬酸络合溶胶-凝胶法可以制备出纳米钙钛矿型结构的催化剂,颗粒细度分布在10～50 nm、比表面积在90m2·g-1,催化剂的活性与Cu的取代量焙烧温度有关,当焙烧温度在700℃、x=0.2时催化剂对CO的氧化具有较高的活性.     

Synthesis and electrochemical characteristics of xLi2MnO3·（1-x）Li- （Ni1/3Co1/3Mn1/3）O2 compounds

xLi2MnO3·(1-x)Li(Ni1/3Co1/3Mn1/3)O2 (x=0.25, 0.40, 0.55) compounds were prepared by low-heating solid state reaction. In the voltage range of 2.70-4.35 V, the discharge capacity of the electrode decreased with the increase of x, with a better cyclability. However, when cycled between 2.7 and 4.6 V, the cathodes delivered much larger capacities and their capacities increased with the introduction of Li2MnO3. Moreover, it was found that the discharge capacity gradually increased with the cycle number. The rea...     

水热合成La1-x-yCayAxMnO3的磁热性能

采用水热合成法制取了钙钛矿型La1-x-yCayAxMnO3(A为Sr或Ba)化合物粉末.在1.4 T的磁场下,利用自制的ΔTad-T曲线测量仪测得其磁热效应,发现A离子的掺杂量x会使居里温度TC增加.依据拟合的曲线规律,控制化合物的成分,制得室温附近不同掺杂的镧锰氧化合物样品,估算的居里温度与实测值接近.