Magnetocaloric properties of La0.6Ca0.4MnO3

A theoretic work on magnetocaloric properties of the polycrystalline La_0.6Ca_0.4MnO₃ system near a second-order phase transition from a ferromagnetic to a paramagnetic state is presented. The value of the magnetocaloric effect has been determined from the calculation of magnetization as a function of temperature under different external magnetic field shifts. The magnetic entropy change ?S _M reaches a peak of about 3 J kg^?1 K^?1 at 266 K upon 1.60 KA/m applied field variation. The ?S _M distribution is much more uniform than that of gadolinium, which is desirable for an Ericson-cycle magnetic refrigerator, which is beneficial for the household application of active magnetic refrigerant materials.     

钙钛矿型锰酸盐(Sm_(0.4)Ca_(0.6)MnO_3)的水热合成及其电性能

以Sm(NO3)3,Ca(NO3)2,KMn O4和Mn Cl2为原料,用水热法合成了混合价态的钙钛矿型锰酸盐Sm0.4Ca0.6Mn O3(1),其结构和性能经SEM,元素分析,TGA,XRD,XPS,I-V曲线和变温电阻表征。结果表明:1为黑色立方晶体,正交晶系,空间群Pnma;1的晶胞参数a=5.336(6),b=5.341(7),c=7.491(6),V=213.56(3)3;1的热稳定性较好,有半导体特性和负磁电阻效应。     

Twinning and structure of Eu0.6Sr0.4MnO3

The crystal structure of europium strontium manganese trioxide, Eu_0.6Sr_0.4MnO₃, has been refined using a multiply twinned single crystal containing six twin components. The MnO₆ octa­hedra show Jahn–Teller distortions with nearly fourfold symmetry, but the octa­hedral tilting scheme reduces the crystal symmetry to ortho­rhom­bic (space group Pbnm). The refinement of site occupancies and the analysis of difference Fourier maps show that the Eu³⁺ and Sr²⁺ cations occupy different crystallographic positions with eightfold and twelvefold coordination, respectively.     

Pr0.6-xNdxSr0.4FeO3-δ电极材料的光谱及性能研究

以柠檬酸-硝酸盐自蔓延燃烧法合成了ABO₃型钙钛矿结构的Pr_0.6-xNd_xSr_0.4FeO_3-δ(x=0.0～0.6)系列稀土复合氧化物粉体。利用傅立叶变换红外光谱(FTIR)和激光共焦拉曼光谱(LRS)对产物的晶体结构进行了表征。分别采用热膨胀仪测定烧结陶瓷体的热膨胀系数(TEC)；TG-DTA记录材料的热稳定性；XRD研究阴极材料与中温电解质Sm_0.2Ce_0.8O_1.9(SDC)及La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-δ(LSGM)的化学相容性；SEM观察阴极/电解质复合材料的断口形貌。结果表明，该系列样品在高、低温热循环过程中化学稳定、晶型稳定；在室温至1 100 ℃范围内的平均热膨胀系数为1.16 × 10^-5 K^-1，与SDC及LSGM的热膨胀系数十分接近。阴极/电解质混合粉体1 200 ℃煅烧10 h，XRD未检测到新物质；SEM显示复合层断面界面清晰，没有相互扩散现象。该体系有望成为以SDC或LSGM为电解质的中温固体氧化物燃料电池合适的阴极材料。     

La0.6Sr0.4MnO3纳米薄膜的制备及其光催化活性

在室温下,采用溶胶-凝胶法和浸渍提拉技术在载玻片基底上制备出了钙钛矿型La0.6Sr0.4MnO3薄膜;采用TG/DTA技术分析了金属羧酸盐凝胶的热分解历程;通过XRD进行了物相分析,并计算了其晶粒尺寸;利用AFM观察了薄膜的形貌特征.实验结果表明,La0.6Sr0.4MnO3薄膜在570 ℃形成,为三方晶系,其平均晶粒度为10.8 am.采用制备出的La0.6Sr0.4MnO3薄膜对多种水溶性染料进行了光催化降解实验,研究发现,该纳米薄膜有较好的光催化效果,在9 h内对酸性红A、酸性橙Ⅱ、弱酸性黄C-3GN、直接绿BE、弱酸性蓝C-RL的脱色率分别达到95.56%,89.70%,97.56%,98.40%和81.16%.     

High surface area nano-sized La0.6Ca0.4MnO3 perovskite powder prepared by low temperature pyrolysis of a modified citrate gel

Single phase nanocrystalline La_0.6Ca_0.4MnO₃ powder was synthesized by both the usual and a modified citrate gel precursor method, and the effects on the formation of homogeneous nano-sized powder with a perovskite structure were investigated. In the modified method, single phase La_0.6Ca_0.4MnO₃ powder with an average particle size of 17.2 nm was obtained when the powder was pyrolyzed at 520°C for 2 h. Its specific surface area was 40.7 m² g⁻¹, about 4-fold larger than that of powder made by the usual citrate gel method.      

Electrochemical characteristics of La0.6Sr0.4CoO3-δ, Pr0.6Sr0.4CoO3-δ and Gd0.6Sr0.4CoO3-δ on Ce0.85Sm0.15O1.925 electrolyte

Cyclic voltammetry, chronoamperometry and electro-chemical impedance have been used for the analysis of the following medium temperature half-cells: Ce_0.85Sm_0.15O_1.925| La_0.6Sr_0.4CoO_3-δ, Ce_0.85Sm_0.15O_1.925| Pr_0.6Sr_0.4CoO_3-δ and Ce_0.85Sm_0.15O_1.925| Gd_0.6Sr_0.4CoO_3-δ. The influence of the atomic mass of the A–site cation in the perovskite cathode on the oxygen reduction kinetics has been discussed. The total polarisation resistance, obtained from the Z′′, Z′-plots, increases with the rise of atomic mass of the cation in the A-site position. Two different time constants have been obtained for the oxygen electroreduction process, and the replacement of La³⁺ by Gd³⁺ in the cathode material decreases somewhat the surface catalytic activity, but the noticeably higher low-frequency series resistance, i.e. mainly diffusion-like mass transfer resistance, values have been obtained. However, the mainly diffusion-limited process at T≤773 K for Gd_0.6Sr_0.4CoO_3-δ and the kinetically mixed process (diffusion + charge transfer) for Pr_0.6Sr_0.4CoO_3-δ and La_0.6Sr_0.4CoO_3-δ have been established. At higher temperature (T≥993 K) and more negative potentials, the O₂ reduction process is limited mainly by the heterogeneous charge transfer step. Presented at the fourth Baltic Conference on Electrochemistry, Greifswald, March 13–16, 2005.     

Pr0.6-xNdxCa0.4FeO3-δ体系复合氧化物的Pechini法合成与表征

采用Pechini法合成了Pr0.6-xNdxCa0.4FeO3-δ（x=0．0，0．2，0．3，0．4，0．5，0．6）系列复合氧化物粉体，用FT-IR，BET，XRD，TG-DTA，SEM等对产物形成过程及微结构进行了表征。结果表明，所合成的系列产物平均粒径均小于100nm，粉体烧结活性高，1200℃下烧结2 h样品的相对密度达到95％。所有产物在900℃下煅烧2 h即形成正交钙钛矿结构的单相固溶体；A位双稀土元素的存在对产物的晶型无影响。随着样品Pr／Nd比例的减小（x值增大），XRD衍射峰宽度有增大的趋势。采用直流四端子法测量了烧结体在中温（450～800℃）区的电导率，A位双稀土样品的电导率优于单一稀土样品，Pr0.1-Nd0.5Ca0.4FeO3-δ样品的电导率最高。     

Phase equilibria in Pr0.7Cd0.3MnO3 and Pr0.7Bi0.3MnO3

A solid state synthesis and phase transitions of solid solutions Pr_0.7Cd_0.3MnO₃ (PCM) and Pr_0.7Bi_0.3MnO₃ (PBM) have been studied within 20–1150°C temperature range. At room temperature, PCM and PBM phases are rhombic within Pnma space group. At high temperatures, Mn-O bonds in PCM are highly anisotropic, the anisotropy becoming insignificant at low temperatures.     

Influence of heat treatment on the magnetic and magnetocaloric properties in Nd0.6Sr0.4MnO3 compound

In the present investigation, the effect of annealing temperature on the structural, electrical transport and the magnetocaloric effect of Nd_0.6Sr_0.4MnO₃ manganites have been studied. Rietveld refinement of XRD data reveals that all samples are single phase with a space group (Pnma). Heat treatment enhances the grain size and decreases the porosity. All samples suffer Curie transition from ferromagnetic to paramagnetic. Magnetocaloric parameters have been determined by the analysis of isothermal M (H) curves around Curie temperature (ΔH = 2 T) for samples. Heat treatment enhances magnetic entropy, which reaches a maximum at T_an = 900 °C. In addition, the rate cooling power records highest value at T_an = 700 °C.     

Tunable Microwave Dielectric Properties of Ca0.6La0.8/3TiO3 and Ca0.8Sm0.4/3TiO3-Modified (Mg0.6Zn0.4)0.95Ni0.05TiO3 Ceramics with a Near-Zero Temperature Coefficient

The microstructures and microwave dielectric properties of (Mg_0.6Zn_0.4)_0.95Ni_0.05TiO₃ with Ca_0.6La_0.8/3TiO₃ and Ca_0.8Sm_0.4/3TiO₃ additions prepared by the solid-state method has been investigated. The crystallization and microstructures of these two mixed dielectrics were checked by XRD, EDX, BEI, and SEM to demonstrate two phase systems. Furthermore, the tunable dielectric properties can be achieved by adjusting the amounts of Ca_0.6La_0.8/3TiO₃ and Ca_0.8Sm_0.4/3TiO₃ additions, respectively. After optimization of processed parameters, a new dielectric material system 0.88(Mg_0.6Zn_0.4)_0.95Ni_0.05TiO₃-0.12Ca_0.6La_0.8/3TiO₃ possesses a permittivity (ε_r) of 24.7, a Qf value of 106,000 (GHz), and a τ_f value of 3.8 (ppm/°C), with sintering temperature at 1225 °C for 4 h. This dielectric system with a near-zero temperature coefficient and appropriate microwave properties revealed a high potential for high-quality substrates adopted in wireless communication devices.     

Spectroscopic properties of Pr3+ ions in a PbWO4 single crystal

Site-selective fluorescence laser spectroscopy of Pr (3+) ions in lead tungstate single crystal were investigated at temperatures from 10 to 300 K. The site-selective emission spectra and fluorescence decays from the (3)P J ( J = 0, 1, 2) and (1)D 2 states were analyzed. The (3)P J ( J = 0, 1, 2) level shows its predominantly radioactive character with the typical greenish-blue luminescence ascribed to (3)P J transition. The emission from the (1)D 2 level is only observed when this level is directly excited. The decay kinetic of the (1)D 2 level was measured under site-selective excitation and discussed in terms of cross-relaxation. The up-conversion emission from levels (3)P 1 and (3)P 0 following excitation of the (1)D 2 state was observed in the PbWO 4 crystal between 10 and 300 K. The main up-conversion mechanism, together with the understanding the quenching of the (1)D 2 fluorescence in this Pr (3+) heavily doped PbWO 4 were discussed. The presence of the complex structures of the emission spectra and different decay profiles indicate that several processes contribute to the quenching of the (1)D 2 fluorescence of Pr (3+) ions. It was found that the up-conversion fluorescence intensity had a quadratic dependence on the laser input power. The temporal behavior of the up converted emission indicates that an energy-transfer up-conversion is the dominant process.     

Ag/La0.6Sr0.4MnO3 Catalysts for Complete Oxidation of Alcohol Fueled Car Exhausts

Alcohol fuel has been suggested as an alternative for car operation to reduce gasoline consumption^[1]. However, being different from that of gasoline car, alcohol-fueled car exhaust principally contains unburned alcohol and formaldehyde/acetaldehyde^[2]. These volatile C₁/C₂ organics may have an undesirable impact on air quality. Most of the existing catalysts for complete oxidation of alcohol are precious metal catalysts supported by γ-Al₂O₃^[2,3].     

低浓度甲烷甲醇深度氧化Ag/La0.6Sr0.4MnO3催化剂

用柠檬酸溶胶－凝胶法制备钙钛矿型Ｌａ０．６Ｓｒ０．４ＭｎＯ３氧化物,并用Ａｇ对其进行修饰,制得Ａｇ／Ｌａ０．６Ｓｒ０．４ＭｎＯ３系列催化剂。结果表明,６％Ａｇ／Ｌａ０．６Ｓｒ０．４ＭｎＯ３催化剂上甲烷或甲醇氧化转化９５％时的反应温度Ｔ９５可低至７３５Ｋ（对ＣＨ４）或４２１Ｋ（对ＣＨ３ＯＨ）;适量Ａｇ的负载修饰并不改变催化剂基质氧化物Ｌａ０．６Ｓｒ０．４ＭｎＯ３的纳米级钙钛矿型结构;Ａｇ的掺杂诱使催     

相分离La0．33Pr0．34Ca0．33MnO3薄膜体系中的交换偏置效应

在相分离La0．33Pr0.34Ca0．33MnO3薄膜体系中发现了大的交换偏置效应．在4K时,交换偏置场的大小达到了约1kOe．交换偏置效应可能源自薄膜内禀的电子相分离特性或薄膜的表面效应．交换偏置效应表现出强的温度、冷却磁场以及厚度依赖的关系．     

The relation between structural features and electrochemical activity of MnO2 nanoparticles synthesized from a polyol-made Mn3O4 precursor

A simple hybrid synthesis processing method was developed to synthesize γ-MnO₂ nanocrystalline particles. The polyol method was modified by the addition of nitric acid in order to allow the synthesizing of single-phase Mn₃O₄ in a large scale. In the sequence, the acid digestion technique was used to transform Mn₃O₄ into γ-MnO₂. Structural and morphological characterization was carried out by X-ray diffractometry, Infrared and Raman spectroscopy, thermogravimetric analysis, nitrogen adsorption isotherm, scanning electron microscopy, and transmission electron microscopy. The electrochemical properties were investigated by cyclic voltammetry and galvanostatic charge–discharge measurements. The synthesized material exhibits a specific capacitance of 125.1 F?g^?1 at a mass loading of 0.98 mg?cm^?2. The relation between structural features and electrochemical activity is discussed by comparing the synthesized material with commercial electrolytic manganese dioxide.     

Relationship between crystal packing and high electron mobility in the single crystal of thienyl-substituted methanofullerene

The X-ray crystal structure of 1-(3-methoxy-carbonyl)-propyl-1-thienyl-[6,6]-methanofullerene (ThCBM) was determined and the electron mobility of the single crystal was measured using a TRMC method to reveal high electron mobility (2 cm(2) V(-1) s(-1)) along the long axis (a-axis) and its remarkable anisotropy (7 times).     

Nanoscale current modulations in Pr(0.7)Ca(0.3)MnO(3) thin films

Many theoretical and experimental efforts have been focused on the origin of the electric-pulse-induced resistance change effect. However, there are still various reports of the origin supporting either the bulk nature or the interface nature. To resolve the controversies, nanoscale electronic measurements may provide essential clues. In this work, we report microscopic electrical properties of Pr(0.7)Ca(0.3)MnO(3) thin films. The resistance of a single-crystalline grain is not homogeneous in nanometer scale. We deduce that nanoscale inhomogeneity is related to the periodic relaxation of substrate-induced strain, which is caused by the lattice mismatch between the substrate and the thin film.     

Synthesis and description of SrSn0.6Ln0.4O3 perovskite pigments

Inorganic pigments containing lanthanides based on pseudo cubic structure of SrSnO₃ have been prepared by solid state reaction between SrCO₃, SnO₂ and lanthanide oxides (Tb₄O₇, Pr₆O₁₁, CeO₂) in the temperature range 1300–1550°C. The resultant materials were characterised by XRD, TG-DTA and colourimetric techniques were used. The most interesting colour properties were provided by SrTb_0.4Sn_0.6O₃ prepared by firing at temperature 1500°C which has light yellow-green colour hue. The increase of temperature 1300–1500°C caused the creation of pigments with deeper and brighter colour hue. Colour properties of the samples prepared by calcination at 1550°C were of inferior quality due to structural changes from pseudo cubic to orthorhombic system.