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-xMn1-x CrxO3,is performed with x changing from 0.04 to 0.08 through measurements of zero-field resistivity (ρ) magnetoresistance(MR) and ac susceptibility (x) as functions of temperature(T). For the second group,a single insulator-metal transition was characterized by the resistivity maximum appears in ρ 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 of x-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 Mn3+ ion and Cr3+ ion.     

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.     

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.     

Mn位Cr掺杂对亚锰酸盐La0.7Ca0.3MnO3低场磁电阻影响

为了研究钙钛矿亚锰酸盐在较低磁场下的磁电阻效应,采用固相反应法制备了亚锰酸盐多晶样品La_(0. 7)Ca_(0. 3)Mn_(1-x)Cr_xO_3(x=0,0. 1),测量了两个样品在未加磁场和加0. 25 T磁场的电阻-温度曲线及磁电阻-温度曲线,分析了Mn位Cr掺杂对样品低场磁电阻效应的影响。实验结果表明,随着Cr掺杂量从x=0增加到x=0. 1,样品的金属-绝缘体转变温度逐渐向低温推移,磁电阻峰值温度由T_P≈220 K下降到T_P≈190 K。在0. 25 T磁场下,样品在液氮温区具有较明显的磁电阻效应。     

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.     

Magnetic properties of Fe3（1-x）Cr3xC alloys

The magnetic properties of Fe33(1-x)Cr3xC alloys with x=0.05, 0.1, 0.15, and 0.2, which crystallize in the cementiteFe3C-type structure with space group Pnma, were investigated by means of magnetization measurements. These alloys show tem-perature-induced second-order magnetic phase transitions. The Curie temperature (Tc) of these alloys decreases with increasing x. The isothermal magnetic-entropy changes of these alloys were derived from the magnetic isotherms measured with increasing tem-x = 0.05 in a magnetic field change from 0 to 1 T and 0 to 5 T, respectively.     

Dielectric Properties of （AgxNa1-x）（NbyTa1-y）O3 System Prepared by Liquid Method

The dielectric properties of （AgxNa1-x）（NbyTa1-y）O3 were investigated, and its dielectric loss and capacitance were measured. The dielectric properties of nanometer （AgxNa1-x）（NbyTa1-y）O3 ceramic prepared by liquid method were better than that by conventional solid method. The average grain size of the nanometer powder（34 nm） obtained by citrate-gel method was small near 500 nm and homogeneous and the microstructure was dense and uniform. In addition, the sintering temperature had a great effect on properties. The dielectric properties of resultant samples were as follows： ε〉500, tgδ〈6 10^-4, αc〈 10 ppm/℃, ρv〉1 012Ω·cm.     

空位掺杂La（1-x）2／3Ca1／3MnO3的结构及磁电阻效应

利用标准的固相反应法在1200℃烧结了La(1-x)2/3Ca1/3MnO3(x=0,0.02,0.04,0.08,0.10)样品,冷却后,取出部分在1350℃进行再烧结。利用X射线衍射(XRD)和扫描电镜(SEM)对其晶体结构及表面微观结构进行了研究。X射线衍射测量分析表明样品均为单相,单胞仍然具有正交对称性结构(空间群为Pnm a),随着掺杂浓度的增加,晶格常数和晶胞体积逐渐减小。通过扫描电镜研究表明,样品随着掺杂浓度增加,晶粒逐渐增大,均匀性变好;样品在1350℃再烧结条件下,平均粒度要大,空隙度变小。样品随着掺杂浓度的增加,电阻在逐渐增大,磁电阻在逐渐减小。     

Structure and Electric Properties of （1-x）（Bi1/2Na1/2） TiO3-xBaTiO3 Systems

The structural, dielectric and piezoelectric properties of （1-x）（Bi1/2Na1/2） TiO3-xBaTiO3 ceramics were investigated for the compositional range, x=0.02, 0.04, 0.06, 0.08, 0.10. The samples were synthesized by a conventional solid-state reaction technique. All compositions show a single perovskite structure, and X-ray powder diffraction patterns can be indexed using a rhombohedral structure. Lattice constants and lattice distortion increase while the amount of BaTiO3 increases. The X-ray diffraction results show the morphotropic phase boundary （MPB） of （1-x）（Bi1/2Na12） TiO3-xBaTiO3 exists in near x=0.06-0.08. Temperature dependence of dielectric constant eT33/ε0 measurement reveals that all compositions experience one structural phase and two ferroelectric phases transition below 400℃： rhombohedral （or rhombohedral plus tetragonal） ferroelectric phase ←→ tetragonal antiferroelectric phase ←→ tetragonal paraelectric phase. Relaxor behaviors exist in the course of ferroelectric to antiferroelectric phase transition. Dielectric and piezoelectric properties are enhanced in the MPB range for （ 1-x）（Bi1/2Na1/2）TiO3-xBaTiO3.     

单一基质白光荧光粉Ba1.31Ca0.64-x SiO4：0.02Eu2＋,0.03Mn2＋,xRe3＋（Re3＋=La3＋,Sm3＋）的研究

采用高温固相法合成单相白色荧光粉Ba1.31Ca0.64-xSiO4：0.02Eu2＋,0.03Mn2＋,xRe3＋（Re3＋ =La3＋,Sm3＋）,研究掺杂La3＋,Sm3＋的荧光粉的光谱特性.XRD结果表明合成的样品具有Ba1.31 Ca0.69SiO4晶相结构.荧光粉的发射光谱由蓝绿光波带（430～550 nm）和橙红光波带（560 ～650 nm）组成,分别归属于Eu2＋取代Ba2＋ （Ca2＋）格位的5d-4f跃迁和Mn2＋取代Ca2＋格位的4T1-6A1跃迁.La3＋和Sm3＋能够提高荧光粉的发光强度,且La3＋效果较好.合成的白光荧光粉具有较好的光色参数,色温Tc=4 478～5 753 K,显色指数Ra均大于80.0.     

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...     

Synthesis and luminescence properties of Eu3＋, Sm3＋ doped （YxGd1-x）2O3： Si4＋, Mg2＋ long-lasting phosphor

A novel red long-lasting phosphor,(Y1-xGdx)2O3:Eu3+,Sm3+,Si4+,Mg2+,was synthesized by the co-precipitation method using oxalate precipitation as the precursor.X-ray diffraction(XRD),scanning electronic microscopy(SEM),integrated thermal analyzer(TG),and photoluminescence spectra(PL) as well as the ST-900PM weak light photometer were used to study the synthesis conditions,morphology,luminescence properties,and the decay time of the phosphor.The XRD results show that the products synthesized at 1400°C for 4 h...     

Structure,Electrical Conducting and Thermal Expansion Properties of Ln0.6Sr0.4Co0.8Fe0.2O3 （Ln = La,Pr, Nd,Sm） Ceramics

Ln0.6Sr0.4Co0.2Fe0.2O3 （Ln=La, Pr, Nd, Sm） perovskite-type complex oxides were synthesized using a glycine-nitrate process, and the structure, electrical conducting and thermal expansion properties of the resulting ceramics were examined with regard to the nature of the lanthanide cations. The results indicated that the La, Pr and Nd specimens had a rhombohedral symmetry, while an orthorhombic structure was determined for the Sm specimen. The pseudo-cubic lattice constant decreased with smaller lanthanide cations. It was found that the electrical conducting properties declined with decreasing lanthanide cation size. Fortunately, all the compositions remained rather high electrical conductivities exceeding 650 Ω ^-1m·cm^-1 in the intermediate temperature range （600-800 ℃）. An appreciable thermal expansion increase at high temperatures was detected for all the compositions. Decreasing the size of the lanthanide cations resulted in an increase of thermal expansion. With respect to the high electrical conductivities, the Ln0.6Sr0.4Co0.8Fe0.2O3 oxides are considered to be acceptable as mixed conducting component in composite cathode designs together with doped ceria electrolytes.     

The Effect of Bi2O3 on the Structure and Microwave Dielectric Properties of Ba6-3xNd8＋2xTi18O54 System（x=2/3）

The structures and dielectric properties of Ba6-3xNd8＋2xTi18O54 system（x=2/3） doped with different contents of Bi2O3, whose final molecular formula is Ba6-3x（Nd1-yBiy）8＋2xTi18O54 were investigated. It is indicated that the dielectric constant increases greatly whereas Q value（f0=4 GHz） decreases with the increase of Bi2O3 content. However, the temperature coefficient could be controlled below 0±30×10^-6/℃ in the experiment. These phenomena are related to the appearance of a new phase, Bi4Ti3O12, which has high dielectric constant. Also, that Bi^3＋（0.13 nm） substitutes for Nd^3＋（0.099 5 nm） will increase the unit cell volume, which will lead to the enlargement of the octahedron B site occupied by Ti^4＋. So the spontaneous polarization of Ti^4＋ ions will be strengthened. Besides, Bi^3＋ will fill up some vacancies which Ba^2＋ or Nd^3＋ ions leave in two A1 sites and four A2 sites. More positive ions polarize, which also contributes to higher dielectric constant. The samples got with the optimium properties are sintered at 1 200 ℃ for 4 h, when y=0.25, ε≈110, Q≈5 400（f0=4 GHz）, TCC=-4.7×10^-6/℃; When y=0.3, ε≈120, Q≈5 000（f0=4 GHz）, TCC=-24×10^-6/℃.     

Structure and Mixed Electronic-ionic Conducting Properties of La0.6Sr0.4Co1-yFeyO3（y= 0-1.0） Ceramics Made by a Citrate Method

La0.6Sr0.4Co1-yFeyO3（y= 0-1.0） powders were synthesized by a citrate method, and the structure and mixed electronic-ionic conducting properties of the resulting ceramics were investigated. The synthesized La0.6Sr0.4Co1-yFeyO3 powders have a pure perovskite structure and consist of uniform and fine particles. A perovskite struciure with rhombohedral symmetry was certified for the La0.6Sr0.4Co1-yFeyO3 ceramics. The increase of Co/Fe ratio significantly promoted the grain growth and microstructural densification. The La0.6Sr0.4Co1-yFeyO3 compositions with relatively higher Co/Fe ratio exhibit superior mixed conducting properties. The electronic structure and microstructure of the ceramics are responsible for the variation of the mixed conducting properties with Co/Fe ratio.