Synthesis of lanthanum–strontium manganites by oxalate-precursor co-precipitation methods in solution and in reverse micellar microemulsion

Nanostructured lanthanum–strontium manganites were synthesized using two different co-precipitation approaches, one in bulk solution, and the other in reverse micelles of CTAB/1-hexanol/water microemulsion. In both cases, precursor cations were precipitated by using oxalic acid. The properties of the materials synthesized by using these two methods were compared in order to reveal potential advantages of the microemulsion-assisted approach. The influence of the annealing conditions on the properties of synthesized manganites was investigated by using X-ray diffraction, transmission electron microscopy, differential thermal analysis, thermogravimetric analysis and magnetic measurements.     

Preparation of Ce-Zr-O solid solution

A single phase solid solution of Ce-Zr-O can be made by using NH₄HCO₃ solution as precipitating agent. The influence of preparation conditions, such as pH, Zr⁴⁺/(CO₃ ^2-+HCO₃ ^-) and Ce³⁺/Zr⁴⁺ ratio on the formation of the solid solution were investigated. The results show that a single phase Ce-Zr-O solid solution can be formed only under a narrow window of preparation conditions, indicating that some compounds are formed in the precipitating process. The compound may contain Ce³⁺, Zr⁴⁺, CO₃ ^2-, HCO^3-, and OH^-. The solid solution so prepared can be described as Ce_0.37Zr_0.63O₂. This revised version was published online in August 2006 with corrections to the Cover Date.     

The electrochemical evaluation of antipsychotic drug (promethazine) in biological and environmental samples through samarium cobalt oxide nanoparticles

In this work, we developed a perovskite structured samarium cobalt oxide nanoparticles (SmCoO₃ NPs) with the aid of the co-precipitation method. The rare earth metal (Sm) and cobalt oxide combined to form a perovskite lattice structure. One-pot route synthesized SmCoO₃ NPs were scrutinized successfully through various physicochemical techniques. Concerning its effective thermal stability and electrical properties, the synthesized SmCoO₃ NPs have been effectively implemented in the electrochemical evaluation of promethazine hydrochloride (PHY) using cyclic voltammetry. The electrochemical detection of PHY was performed through SmCoO₃ NPs-modified glassy carbon electrode (GCE) and unmodified GCE. The electron transfer kinetics, effect of scan rate, the influence of pH, electroactive surface area, selectivity, and sensitivity have been studied. The electron charge transfer rate (R_ct) and electrolyte resistance (R_s) were calculated to be 105.59 (Ω) and 150 (Ω) in the ferricyanide probe, indicating great facilitation of the electron transfer between PHY and SmCoO₃ NPs deposited on the electrode surface. Further, the optimized SmCoO₃-modified GCE exemplifies excellent selectivity, storage stability, reproducibility, repeatability, detection limit (5 nM), sensitivity (0.594 μA μM^?1 cm^?2), and wide consecutive linear ranges, respectively. Besides, the proposed method has been effectively employed for the detection of PHY in the various real samples which reveals good recoveries of 95.40–99.17%.     

新型复合共沉淀法制备高能量/高功率型锂离子二次电池用5V正极材料LiNi_(0.5)Mn_(1.5)O_4及其电化学性能

在传统的固相法的基础上开发了新型复合共沉淀法制备LiNi0.5Mn1.5O4材料.新型复合共沉淀法采用(NH4)2CO3和(NH4)2C2O4共同作为沉淀剂,通过控制共沉淀反应条件,得到了具有均匀球形形貌的沉淀物颗粒.再通过与饱和氢氧化锂溶液的水热反应及高温反应,最终制备出具有球形次级形貌和纯相尖晶石结构的LiNi0.5Mn1.5O4材料.电化学测试表明,制备的LiNi0.5Mn1.5O4具有优异的电化学性能,其初始容量达到了141.4mAh·g-1.在0.3C、1C和3C倍率下经过200次循环后的容量分别为136.0 mAh·g-1(96.3%)、128.6 mAh·g-1(94.4%)和113.9 mAh·g-1(91.1%).通过高温反应及特殊的冷却处理,LiNi0.5Mn1.5O4在4.0 V低压区平台的容量损失得到了有效抑制.更重要的是,通过控制合成过程中的关键步骤,可实现半定量化控制材料结构中的原子有序排布程度,进而得到具有高能量密度和高功率密度的两种LiNi0.5Mn1.5O4材料,其能量密度和功率密度分别达到了648.6 mWh·g-1和7000 mW·g-1以上.     

Microwave-assisted synthesis and characterization of Bi-substituted yttrium garnet nanoparticles

Bi-substituted yttrium iron garnet (Bi-YIG, Bi_1.8Y_1.2Fe₅O₁₂) nanoparticles were prepared by microwave-assisted co-precipitation as well as conventional co-precipitation using ammonia aqueous solution as precipitant. The nanoparticles were characterized by thermal gravity-differential thermal analysis, X-ray powder diffraction, transmission electron microscopy, dynamic light scattering and vibrating sample magnetometer, respectively. The Faraday rotation of Bi-YIG modified PMMA slices was also investigated. Results demonstrate that the Bi-YIG nanoparticles prepared by microwave-assisted co-precipitation show smaller particle size and higher Faraday rotation than those prepared by conventional co-precipitation.     

Nano-sized Cu6Sn5 alloy prepared by a co-precipitation reductive route

Nano-sized Cu₆Sn₅ alloy powders were prepared by a co-precipitation reductive route using a hydrothermal method at 80 °C. The nano-size and morphology of the synthesized Cu₆Sn₅ alloy powders were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The obtained morphologies, chemical compositions are comparatively discussed. A variety of synthesis parameters, such as time, capping agent and sort of reductant, has an effect on the morphology of the obtained materials, and will be particularly highlighted.     

Effect of substitution of K ions on the structural and electrical properties of nanocrystalline MgAl2O4 spinel oxide

Potassium substituted nanosized magnesium aluminates having a nominal composition Mg_1−xK_xAl₂O₄ where x=0.0, 0.25, 0.5, 0.75, 1.0 have been synthesized by the chemical co-precipitation method. The samples have been characterized by means of X-ray diffraction (XRD), scanning electron microscope (SEM), and dc electrical resistivity measurements. The XRD results reveal that the samples are spinel single phase cubic close packed crystalline materials. The calculated crystallite size ranges between 6 and 8 nm. The behaviour of the lattice constant seems to deviate from the Vegard's law. While X-ray density clearly increases, the bulk density and consequently, the percentage porosity do not exhibit a significant change on increasing the K⁺ content. The SEM micrographs suggest homogeneous distribution of the nanocrystallites in the samples. The dc electrical resistivity exhibits a typical semiconducting behaviour. Substitution of a Mg²⁺ ion by a K⁺ ion provides an extra hole to the system, which forms small polaron. Thermally activated hopping of these small polarons is believed to be the conduction mechanism in the Mg_1−xK_xAl₂O₄. The activation energy of hopping of small polarons has been calculated and found K⁺ ions content dependent.     

Preparation and magnetic properties of barium ferrites substituted with manganese, cobalt, and tin

Barium ferrites substituted by Mn-Sn, Co-Sn, and Mn-Co-Sn with general formulae BaFe_12−2xMn_xSn_xO₁₉ (x=0.2-1.0), BaFe_12−2xCo_xSn_xO₁₉ (x=0.2-0.8), and BaFe_12−2xCo_x/2Mn_x/2Sn_xO₁₉ (x=0.1-0.6), respectively, have been prepared by a previously reported co-precipitation method. The efficiency of the method was refined by lowering the reaction temperature and shortening the required reaction time, due to which crystallinity improved and the value of saturated magnetization increased as well. Low coercivity temperature coefficients, which are adjustable by doping, were achieved by Mn-Sn and Mn-Co-Sn doping. Synthesis efficiency and the effect of doping are discussed taking into account accumulated data concerning the synthesis and crystal structure of ferrites.     

Synthesis of nanocrystalline Co-Ni alloys by precursor approach and studies on their magnetic properties

Nanocrystalline Co-Ni alloys with different compositions were prepared by polyol reduction of mixed cobalt nickel hydroxides. The precursors (mixed cobalt nickel hydroxides) were prepared by co-precipitation. Powder X-ray diffraction analysis indicated the formation of fcc phase in the alloys and their crystallite size in the range 17-25 nm. Scanning electron microscopy and transmission electron microscopy studies revealed the morphology of the particles as being close to spherical, and the energy dispersive X-ray analysis showed the stoichiometry of the alloys. The magnetization as a function of field and temperature of the alloys, measured using a superconducting quantum interference device, showed superparamagnetic behavior with negligible coercivity and remanence values.     

NaYF4∶Eu3+, Tm3+, Yb3+材料中Stokes和反Stokes发光研究

合成了Eu3+,Tm3+和Yb3+掺杂的NaYF₄材料。360 nm光激发呈蓝色发光,峰值位于452 nm,对应Tm3+的1D₂→3F₄跃迁;395 nm光激发呈橙色发光,峰值位于591 nm,对应Eu3+的5D₀→7F₁跃迁;409 nm光激发呈红色发光,峰值位于613 nm,对应Eu3+的5D₀→7F₂跃迁;980 nm光激发呈蓝色和红色发光,发光峰位于474和646 nm。蓝光来源Tm3+的1G₄ →3H₆跃迁,红光来源Tm3+的1G₄→3F₄跃迁。在双对数曲线中,蓝光474 nm和红光646 nm的斜率分别为2.1和2.4,在980 nm光激发下,蓝光和红光发射都是双光子过程。还研究了材料的吸收光谱,并利用X射线衍射,扫描电镜测试了材料的物相结构和微观形貌。结果表明：NaYF₄∶Eu3+, Tm3+, Yb3+材料具有较规则的六方相结构,结晶良好。