NdFeB永磁材料的稳定性及应用

本文根据国内外对第三代稀土永磁 NdFe B 材料的系统研究,综合分析了烧结 NdFe B 永磁材料的稳定性,说明它在不同环境下的使用,以期合理地选用。     

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.     

Magnetic domain structures of precipitation-hardened SmCo 2：17-type sintered magnets： Heat treatment effect

The typical magnetic domains of Sm（CObalFe0.25Cuo.07Zr0.02）7.4 magnets quenched through various heattreatment steps have been revealed by using magnetic force microscopy （MFM）. For the specimens in which the nominal c-axis is perpendicular to the imaging plane, the domain configurations change from plate-like for the as-sintered magnet to corrugation and spike-like for the homogenized one, and then to a coarse and finally to a finer domain structure when isothermally aged at 830℃ and then annealed at 400℃. However, only plate-like domains can be detected on the surfaces with the nominal c-axis parallel to the imaging plane. The finer domain （so-called interaction domain） is a characteristic magnetic domain pattern of the SmCo 2：IT-type magnets with high coercivities. Domain walls in a zigzag shape are revealed by means of MFM in final bulk SraCo 2：17-type sintered magnets.     

ZnTe（ZnTe：Cu）多晶薄膜的XPS研究

用共蒸发法在室温下制备了ZnTe及ZnTe：Cu多晶薄膜，测量了电导率温度曲线，发现不掺杂的ZnTe薄膜的暗电导随温度的增加而线形增加，呈常规的半导体材料特征；掺Cu的ZnTe薄膜在温度较低时，lnσ随温度升高而缓慢增加，随后缓慢降低，达到一极小值，当温度继续升高时又陡然增加，呈现异常现象。用XPS研究了N2气氛下退火前后表面状态，发现不掺Cu的ZnTe薄膜呈现富Te现象。掺Cu后Te氧化明显，以ZnTe形式存在的Te明显减少；ZnTe：Cu薄膜中Zn的含量在退火前后变化明显，退火前，Zn主要以ZnTe形式存在，退火后Zn原子向表面扩散，使表面成分更加均匀，谱峰变宽；退火时，部分Cu原子进入晶格形成CuxTe相，引起载流子浓度变化，导致ZnTe：Cu多晶薄膜的电导温度关系异常。     

First-Principles Study of Electronic Structure of the Laves Phase ZrFe2

We perform the ab initio calculation for obtaining the density of states and magnetic properties of ZrFe2 Laves phase compound based on the method of augmented plane waves plus local orbital The results indicate that the ferromagnetic state is more stable than the paramagnetic one, but with a slightly larger volume. The 3d - 4d exchange interactions between Fe and Zr electrons lead to the antiparallel coupling for Fe 3d and Zr 4d states, which is responsible for the ferrimagnetic ordering of the compound. The resulting magnetic moment of about 1.98μB for Fe is spatially localized near the Fe site, while around Zr a small but extended negative spin states causes a moment of about -0.44 μB. Moreover, the resulting magnetic moments with the generalized gradient approximation are more consistent with experimental values than that of the local-spin density approximation.     

Hot deformation in nanocrystalline Ndben Feben B backward extruded rings

Radially oriented Nd-Fe-B rings are prepared by backward extrusion of fine grained melt-spun powder. Melt-spun powder with the nominal composition of Nd_30.5Fe_bal.Co_6.0Ga_0.6Al_0.2B_0.9 (wt%) is used as starting material. The effects of process variables, such as deformation temperature (T_d), strain rate (ε) and height reduction (Δh%), on the magnetic properties of the rings are investigated. A scanning electron microscope (SEM) equipped with an energy spectrum device is used to study the metallograph and microfracture of the extruded rings. The B_r and (BH)_max reach the optimum values at T_d=800℃, ε =0.01 mm/s, and Δh% =70%. It is found by SEM observations that the particle boundaries, which seemingly correspond to the interfaces of the starting melt-spun powders, emerge after the corrosion of metallography specimens. This is helpful for studying the effects of powder-powder interface on the local deformation and deformation homogeneity in the rings. For different spatial positions of the extruded rings, there are characteristic metallographies and microfractures. The upper end of the rings has the least deformation and worst texture, and therefore the worst magnetic properties. The magnetic properties in the radial direction increase slightly along the axis from the bottom to the middle, then steeply decrease at the upper end of the ring. The deformation and the formation-of-texturing processes are discussed. The deformation and the texturing formation of melt-spun Nd-Fe-B alloys probably involve grain boundary sliding and grain rotation, the solution-precipitation process and preferential growth of Nd₂Fe₁₄B nanograins along the easy growth a-axis.     

偏振光干涉法消除光纤光栅解调中的交叉敏感现象

提出一种偏振光干涉的光纤光栅应变测量方法,该方法能解决光纤光栅应变和温度测量时的交叉敏感问题。对于钒酸钇晶体偏振光干涉仪,如果选择两个能使干涉仪产生180°相位差的不同中心波长的光纤光栅,一个用于应变测量,一个用于补偿温度,就能很好地解决光纤光栅应变测量时的温度交叉敏感问题。分析了构成偏振光干涉仪的晶体的厚度对应变偏差的影响。理论计算和试验结果显示,当晶体厚度为0.5 mm时温度对应变测量的交叉敏感现象被压缩到了1.6%,相当于0.13με/℃。进一步的仿真分析发现当晶体厚度为0.1 mm时交叉敏感现象将被压缩到0.08%,相当于0.0067με/℃。小的晶体厚度有利于减小交叉敏感现象,但小厚度的晶体加工困难,为此分析了双晶体结构的方案。     

液体密度测量实验改进的研究

利用电动音叉仪测量液体密度,分析原实验仪器存在的不足,对原实验装置做了改进。通过测量水的密度,结果显示改进后的实验仪器不但提高了测量的精确度,而且操作更快捷、方便。     

Fe40—45Cr30—35Co20—25Mo0—4Zr0—2合金微观结构对矫顽力的影响

研究了高矫顽力型FeCrCo合金的磁性和微观结构.实验结果表明，适当的合金成分及热处理 条件可以明显提高FeCrCo合金的矫顽力.通过透射电镜、x射线衍射等手段得出结论：主体元 素含量的提高和微量元素的掺杂可以有效地控制相的组成，磁场热处理导致强磁性相和弱磁 性相的分离，回火后形成起磁硬化作用的调幅结构.该调幅结构中较大的两相成分差有利于 提高FeCrCo合金的矫顽力. 关键词： 矫顽力 调幅分解 磁场热处理 两相结构 成分差     

CdTe太阳电池中起因于Cu的深能级

在CdTe太阳电池中,易引入并形成Cu深能级中心. 本文采用深能级瞬态谱测试法研究了ZnTe背接触和石墨背接触CdTe太阳电池的部分深能级中心. 研究中运用密度泛函相关理论,分析闪锌矿结构CdTe,Cd空位体系和掺Cu体系的电子态密度,计算得出T_d场和C_3v场下Cu²⁺ d轨道的分裂情况. 计算结果表明,CdTe太阳电池中的E_v+0206 eV和E_v+0122 eV两个深中心来源于Cu替代Cd原子. 计算结果还表明,掺入Cu可降低CdTe体系能量. 关键词： 深能级瞬态谱 第一性原理 CdTe Cu杂质