High Field Magnetism of the Spinel Oxide CoAl2O4

We report the results of magnetization and electron spin resonance (ESR) measurements on sintered samples of the spinel oxide CoAl₂O₄ in magnetic fields up to 53 T. In CoAl₂O₄, Co²⁺ (S=3/2) ions make a diamond lattice, indicating naively that no geometrical frustration takes place. This spinel oxide, however, is thought to be in the vicinity of a quantum melting point of the antiferromagnetically ordered state because of no sharp peak in the temperature dependence of specific heat. Magnetization curve at 4.2 K is almost linear in magnetic fields and a broad ESR signal was observed on a straight resonance line with g=2.26, implying an antiferromagnetic long range order or a well developed antiferromagnetic short range order with very small anisotropy.     

X-ray diffraction study of the CuCr2O4-NiFe2O4 system

Phase relations in the Cu_1-xNi_xCr_2(1-x) solid-solution system, containing Jahn-Teller active cations, were studied by powder x-ray diffraction. The solid solutions with jc > 0.5 were found to have a cubic NiFe₂O₄ (Fd3m) structure. In the range 0.1 <x < 0.4, a cubic phase of approximate composition Cu_0.6Ni_0.4Cr_1.2Fe_0.8O₄ was shown to coexist with a tetragonal phase of composition Cu_0.9Cr_1.2Fe_0.2O₄. The results were interpreted under the assumption that the degree of inversion of the spinel phase varies significantly across the morphotropic region. The lattice parameters and degree of inversion of the solid solutions were determined as a function of composition. The distributions of the divalent and trivalent cations over tetrahedral and octahedral sites were tentatively assessed.     

尖晶石LiMn2O4的合成和电化学性能研究

采用高温固相反应法合成具有尖晶石结构的锂离子二次电池正极材料LiMn2O4,进行稀土元素La的掺杂修饰,形成复合氧化物LiMn2-xLaxO4.对材料进行XRD、FESEM、循环伏安、充放电等测试.实验结果表明,合成的材料具有比较标准的尖晶石结构,La元素掺入可以起到扩展锂离子脱嵌通道和稳定材料骨架结构的作用,更加有利于锂离子的迁移,从而有效提高了LiMn2O4的电化学可逆性和循环稳定性.     

正极材料LixMn2O4容量在循环过程中的损失机理研究

正极材料LixMn2O是近几年锂离子电池研究的热点，但其在循环过程中容量衰减是制约锂离子电池商吕化的关键，LixMn2O4的溶解，晶型转变，过充和过放地导致正极材料LixMn2O4循环过程中容量损失的关键因素，概述了近几年在这方面的研究的研究进展，并提出了当前解决问题的一些途径。     

尖晶石型LiMn_2O_4阴极材料电化学性能研究

利用柠檬酸络合法制备锂离子电池正极材料尖晶石型LiMn2 O4,利用X射线衍射、循环伏安、充放电测试、交流阻抗等手段对它进行了研究。发现活性物质在不同的电位下具有不同的电化学特征 ,电位处在平台区时与处在非平台区时相比 ,交流阻抗谱明显不同。电位处于非充放电平台区时 ,高频表现为锂离子电极材料中的固态扩散 ,在充放电平台区时 ,高频表现为电子到达活性物质的通道的阻抗。     

尖晶石LiMn2O4的掺杂研究进展

相对LiCoO2来说，价廉、低毒的尖晶石LiMn2O4作为高能锂离子电池最有潜力的正极材料已经成为市场研究的热点。但是，在充放电过程中其结构的不稳定制约了它的应用前景。为了得到结构稳定的尖晶石，许多研究小组通过掺杂其它元素来改性LiMn2O4。综述了近几年来在这方面的研究进展。     

Spinel Phase Relations in the Fe3O4–CuFe2O4 System

Phase equilibria involving spinel solid solutions, delafossite, and hematite in the Fe–Cu–O system are studied by emf measurements in solid-electrolyte galvanic cells. The results demonstrate that, above 1250 K, Fe₃O₄ and CuFe₂O₄ form a continuous series of solid solutions. At lower temperatures, the solid solution disproportionates with the formation of delafossite and Fe₂O₃, and two spinel solid solutions appear: one based on Fe₃O₄ and the other based on Cu₂FeO₄. The compositions of the spinel phases in equilibrium with delafossite and Fe₂O₃ are determined in the range 1100–1250 K.     

Study of the Magnetic Properties of the Zn-Doped Spinel LiV2O4 Materials

The magnetic properties of spinel Zn _x Li_1?x V₂O₄ systems are studied by using the probability law, and high-temperature series expansions in the range 0≤x≤1. The nearest-neighboring J ₁(x) and the next-neighboring super-exchange J ₂(x) interactions are obtained. The intra-planar and the inter-planar exchange interaction are obtained. The corresponding classical exchange energy for the magnetic structure is obtained. The high-temperature series expansion combined with the Padé approximants method has been applied to the spinel Zn _x Li_1?x V₂O₄ systems to determine the magnetic phase diagram. The critical exponents associated with the magnetic susceptibility γ and with the correlation lengths ν are deduced.     

Study of the Magnetic Properties of the Zn-Doped Spinel CdV2O4 Materials

The magnetic properties of spinel Cd_1?x Zn _x V₂O₄ systems in the range 0≤x≤1 are studied by mean field theory and high-temperature series expansions (HTSE). The nearest neighboring and the next-neighboring superexchange interactions J ₂(x) and J ₂(x) are given. The intra-planar and the inter-planar interaction are deduced. The HTSE theory is applied in the spinel Cd_1?x Zn _x V₂O₄ systems, combined with the Padé approximants method, to determine the magnetic phase diagrams (T _N versus dilution x) in the range 0≤x≤1. The critical exponents associated with the magnetic susceptibility γ and the correlation lengths ν are deduced.     

稀土掺杂锂锰氧化物LiMn2-xNdxO4(X=0.005～0.1)的结构和电性能研究

采用微波与传统加热相结合的方法首次合成了稀土掺杂基锂锰氧化物LiMn2-xNdxO4(x=0.005～0.1)材料,电化学性能测试结果表明材料在掺杂量为x=0.01时表现出最大放电比容量,同时具有很好的循环稳定性,经过100次循环其容量衰减仅为14.9%;XRD测试结果表明在LiMn2O4尖晶石晶格中掺入合适量的Nd对稳定尖晶石骨架结构起重要作用;FTIR分析技术揭示了容量少量衰减的原因.     

Spinel LiMn2O4 nanorods as lithium ion battery cathodes

Spinel LiMn2O4 is a low-cost, environmentally friendly, and highly abundant material for Li-ion battery cathodes. Here, we report the hydrothermal synthesis of single-crystalline beta-MnO2 nanorods and their chemical conversion into free-standing single-crystalline LiMn2O4 nanorods using a simple solid-state reaction. The LiMn2O4 nanorods have an average diameter of 130 nm and length of 1.2 microm. Galvanostatic battery testing showed that LiMn2O4 nanorods have a high charge storage capacity at high power rates compared with commercially available powders. More than 85% of the initial charge storage capacity was maintained for over 100 cycles. The structural transformation studies showed that the Li ions intercalated into the cubic phase of the LiMn2O4 with a small change of lattice parameter, followed by the coexistence of two nearly identical cubic phases in the potential range of 3.5 to 4.3 V.     

添加剂对NiFe2O4尖晶石性能的影响

研究了3种添加剂对NiFe2O4尖晶石性能和微观结构的影响.对试样的体积密度、三点抗弯强度、抗热震性、导电率进行了测试,并结合SEM和EDX进行了微观结构分析.结果表明,添加剂M使试样的体积密度变化最快,含有3%M试样的抗弯强度较纯尖晶石提高了25MPa,添加T的试样热震性最好,添加剂M和T均能提高试样的导电能力.     

尖晶石MgFe2O4纳米粉的水热反萃合成

介绍一种合成尖晶石铁酸镁纳米粉的新方法--水热反萃合成法,并用此法合成了晶粒粒度在12～18nm的MgFe2O4粉体.借助于XRD和TEM测试手段.考察了反萃温度、水相的pH和组成对产物形貌和粒度的影响.结果表明:在190～210℃时,用纯水反萃负载金属铁和镁的混合有机相可以直接得到尖晶石结构、近似球形和粒度分布均匀的MgFe2O4纳米粉体,且不会发生硬团聚.     

Magnetization and cation distribution in CoxMg1-xFe2O4 system

Magnetic parameters such as saturation magnetization (σ _s), coercive force (H _c), remanence ratio (σ _r/σ_s) etc of Co_xMg_1?xFe₂O₄ (0?x?1) ferrites were measured at 300 and 80 K. The values ofσ _s,H _c and (σ _r/σ_s) increased as the content of cobalt increased. The magnetic momentμ _B was calculated using theσ _s data. The cation distribution has been suggested on the basis of these results.     

Hot Isostatic Pressing of MgAl2O4 Spinel Infrared Windows

Optically transparent MgAl₂O₂ spinels have been produced by hot isostatic pressing (HIP). The spinel samples were prepared by hot pressing and subjected to capsule-free HIPing. The hot-pressed samples were made at 1500°C with a pressure from 14 to 41 MPa for 2 to 4 hours. In the HIP process, the pressure ranged from 14 to 207 MPa at 1500°C. The effect of hot isostatic pressure on the bulk density, microstructure and optical properties of the spinel sample were investigated here. The bulk density of the sample increased with HIP pressure and the sample HIPed at 207 MPa resulted in a bulk density of 3·576 g/cm³, about 99·94% of the theoretical density. A bimodal grain size distribution exists in samples HIPed at pressures ≤ 138 MPa. The extent of the abnormal grain growth decreased with pressure. The transparent spinel with uniform and fine grain size of 2 μn was obtained at 207 MPa. The transmission at short wavelength increased significantly with HIPing pressure. The transmittance of the sample HIPed at 207 MPa at a wavelength of 0·7 μn was 72%.     

尖晶石型铁氧体CaxZn1-xFe2O4的制备及其光催化性能研究

采用改进的溶胶-凝胶法制备CaxZn1-xFe2O4粉体。用X射线粉末衍射仪(XRD)对样品进行结构表征,随着Ca2+掺杂量的增加,样品出现CaFe2O4的衍射峰。使用扫描电子显微镜(SEM)对样品进行形貌表征,结果表明样品的形貌呈不规则的颗粒状,且颗粒大小为2μm,并显现出片层堆叠情况。通过对甲基橙进行光催化降解实验,对CaxZn1-xFe2O4粉体的光催化活性进行了研究。结果表明,经过Ca2+掺杂的CaxZn1-xFe2O4样品,光催化活性明显提高。     

The Faraday Effect in CoFe2O4 Spinel Ferrite in the IR Range

Technical Physics Letters - The spectral, temperature, and field dependences of the Faraday effect in the IR spectral range have been studied in single crystals of the CoFe2O4 ferrimagnetic spinel....     

尖晶石LiMn2O4容量衰减的原因及解决方法

尖晶石LiMn2O4被认为是最具发展前景的锂离子电池正极材料,但其容量衰减快和循环性能差是制约其商品化的主要原因.分析了尖晶石LiMn2O4容量衰减快和循环性能差的原因,将其归结为内因和外因;在此基础上,从离子掺杂、表面修饰、电解液改性、合成工艺优化几个方面讨论了改善尖晶石LiMn2O4性能的解决方法.