用一种新的装配方式制备单畴GdBCO超导块材

在顶部籽晶熔渗生长工艺(TSIG)的基础上,采用一种新的装配方式制备单畴Gd-Ba-Cu-O(GdBCO)超导块材,并对所得样品的形貌、微观结构以及超导性能进行了研究.结果表明,应用新的装配方式可以提高液相源块的支撑能力,有效避免样品在热处理过程中的倾斜或坍塌现象,从而提高了样品制备过程的稳定性和可重复性.此外,应用新的装配方式还有助于GdBCO样品的完整生长. 关键词： 熔渗生长 新的装配方式 GdBCO     

二次单畴化制备GdBCO超导块材的方法及其性能

高质量单畴REBa_2Cu_3O_(7-δ) (REBCO)超导块材具有广泛的应用前景,但制备过程中极易产生大量多畴样品,致使成功率明显下降、成本显著提高,并制约其进一步批量化和实用化的进程.受顶部籽晶熔渗生长(TSIG)方法的启发,本文提出了一种对生长失败的GdBCO超导块材重新单畴化织构生长的新方法,即将生长失败的样品进行预处理后作为固相源坯块,然后采用改进后的TSIG法进行二次单畴化织构生长,并成功地制备出了一系列二次单畴化的GdBCO超导样品,同时,对样品的超导性能及微观结构进行了研究.结果表明,所制备的二次单畴化GdBCO超导样品的磁悬浮力均大于30 N,样品的捕获磁通密度均在0.3 T以上,捕获磁通效率高达60%以上,该结果为进一步发展低成本、高效率制备REBCO超导体的新方法提供了科学依据和新思路.     

BaO掺杂对单畴GdBCO超导块材性能的影响

采用改进后的顶部籽晶熔渗生长(M-TSIG)工艺,通过在固相先驱粉体中掺杂不同含量的BaO来有效地抑制GdBCO样品生长过程中出现的Gd/Ba替换现象,从而成功地制备出了一系列单畴Gd BCO超导块材,并且对样品的宏观形貌、磁悬浮力、捕获磁通密度及临界温度等超导性能进行了研究.结果表明,随着BaO掺杂量的增加,样品的熔化温度(T_m)及包晶反应温度(T_p)均出现逐渐降低的趋势;同时,当样品中BaO的添加量在2wt%—4wt%时,可以在一定的程度上有效提高Gd BCO样品的磁悬浮力、捕获磁通密度及临界温度等超导性能.     

BaCuO_(2-δ)添加对单畴GdBCO超导块材性能的影响

本文采用顶部籽晶熔融织构法,研究了BaCuO2-δ添加对单畴GdBCO超导块材性能的影响.实验结果表明,当制备GdBCO超导块材所用粉体的摩尔比为Gd123:Gd211:Gd011=1:0.4:x(x=0,0.1,0.2,0.3,0.4)时,均可制备出单畴GdBCO超导块材.对该系列超导块材磁悬浮力测试的结果表明,BaCuO2-δ的含量对GdBCO超导体的磁悬浮力有明显影响,当BaCuO2-δ的含量x=0.2mol%时样品的磁悬浮力最大,并结合其显微组织分析了BaC-uO2-δ对单畴GdBaCuO磁悬浮力影响的原因.     

BaO掺杂对单畴GdBCO超导块材性能的影响(二)

为了有效地抑制Gd BCO超导块材在生长过程中出现的Gd/Ba替换现象,在前期工作的基础上,本文采用顶部籽晶熔渗生长工艺,通过在固相先驱粉中添加不同含量的Ba O粒子成功地制备出了一系列高性能的单畴Gd BCO超导块材,并且对样品的微观形貌以及临界电流密度进行了研究和分析.结果表明,随着BaO掺杂量的增加,样品中的Gd_(1+x)Ba_(2-x)Cu_3O_(7-δ)固溶体(Gd123ss)相呈现出减少的趋势,并生成了纳米量级的Gd123ss,这对GdBCO超导样品中存在的Gd/Ba替换起到了很好的抑制作用,使得样品中的GdBa_2Cu_3O_(7-δ)(Gd123)超导相有所增加;同时当样品中BaO的添加量在2 wt%—4 wt%之间时,样品的临界电流密度在一定程度上得到了有效提高.     

用顶部籽晶熔渗生长工艺由新成分液相源制备单畴GdBCO超导块材

用R₂O₃(R分别为Gd,Y和Yb),BaCuO₂和CuO配制了三种新成分液相源.利用顶部籽晶熔渗生长工艺,分别用这三种新成分液相源制备了单畴Gd-Ba-Cu-O超导块材,并对所得样品的生长特性和微观结构进行了研究.结果表明,使用新液相源可以缩短实验周期,提高制备效率,并能获得织构度良好的单畴块材.此外,由Y₂O₃或Yb₂O_{3相似文献}   

Ni2O3掺杂对新固相源顶部籽晶熔渗生长法制备单畴GdBCO超导块材超导性能的影响

本文通过在新固相源中添加Ni₂O₃的方法, 采用顶部籽晶熔渗生长工艺(TSIG)制备出组分为(1-x) (Gd₂O₃+1.2BaCuO₂)+x Ni₂O₃、直径为20 mm的单畴GdBCO 超导块材(其中x = 0, 0.02, 0.06, 0.10, 0.14, 0.18, 0.30, 0.50 wt%), 并研究了Ni₂O₃的掺杂量x对样品的表面生长形貌、微观结构、临界温度T_c、磁悬浮力以及俘获磁通密度的影响. 研究结果表明, 当Ni₂O₃的掺杂量x在0–0.50 wt%的范围内时, 均可制备出单畴性良好的样品, 且Ni₂O₃的掺杂对样品中Gd211粒子的分布和粒径没有明显的影响. 在Ni₂O₃的掺杂量x从0增加到0.50 wt%的过程中, 样品的临界温度T_c呈现下降的趋势, 从x=0时的92.5 K下降到x=0.50 wt%时的86.5 K, 这是由于Ni^{3 +}替代GdBCO晶体中Cu^{2 +}所致; 样品磁悬浮力和俘获磁通密度均呈现先增大后减小的变化规律, x=0.14 wt%时, 磁悬浮力达到最大值34.2 N, x=0.10 wt%时, 俘获磁通密度达到最大值0.354 T. 样品磁悬浮力和俘获磁通密度的变化规律与Ni₂O₃的掺杂量x有密切关系, 只有当掺杂量x合适时, Ni³⁺对Cu^{2 +}的替代既不会造成T_c的明显下降, 但又能产生适量的Ni^{3 +}/Cu²⁺ 晶格畸变, 从而达到提高样品磁通钉扎能力和超导性能的效果.     

CeO_2掺杂对单畴GdBCO超导块材性能的影响

本文采用顶部籽晶熔融织构方法(TSMTG),分别制备出了直径为17mm的掺杂和未掺杂CeO2的单畴GdBCO超导块材,其中样品中CeO2的掺杂量为1wt%,并且研究了CeO2的掺杂对样品形貌、微观结构、磁悬浮力、以及捕获磁通的影响.研究表明了CeO2的掺杂影响超导块材的生长速率,在微观形貌上,CeO2的掺杂使样品中Gd2BaCuO5(Gd211)粒子的分布更加均匀且粒度明显变小,其平均粒径约从原来未掺杂的5.49μm减小到1.32μm,并且块材中的气孔也明显减小,从而使样品的磁悬浮力从23.06N增加到31.42N,捕获磁通从0.288T增加到0.354T.这对进一步提高超导块材的性能具有重要的指导意义     

新型第二相粒子Gd_2Ba_4CuFeO_y掺杂对单畴超导块材GdBaCO性能的影响

通过顶部热籽晶熔融织构的方法,我们成功地制备出了掺杂新型第二相微粒xGd_2Ba_4CuFeO_y(x=0,0.002,0.004,0.008,0.02)的单畴超导块材GdBCO.通过扫描电镜观察,我们发现,随着掺杂量的增加,一种带状组织存在于掺杂Gd_2Ba_4CuFeO_y微粒的超导块材中;Gd_2BaCuO_5粒子尺寸减小,分布得更加均匀,而Gd_2Ba_4CuFeO_y微粒可能形成有效的钉扎中心;掺杂一定量的包含磁性粒子的Gd_2Ba_4CuFeO_y微粒不但没有破坏超导块材的超导性能,反而增强了超导块材的磁通捕获能力和临界电流密度,超导块材的最大磁通捕获量达到0.16T,临界电流密度TC最大值达到6.4×10~4 A/cm~2,使超导块材的超导性能得到明显改善.实验结果对于研究含磁性粒子的第二相添加提高超导块材的性能有着重要的意义.     

一种实时测量大尺寸REBCO超导块材三维空间磁场及温度分布的装置北大核心CSCD

由于单畴RE-Ba-Cu-O(简称REBCO,其中RE为稀土元素:Nd,Y,Gd,Sm)超导块材具有较高的捕获磁场和较大磁悬浮力等优良的特点,使得其在超导磁悬浮,超导磁体,储能飞轮等高新技术领域有着广泛的应用前景.然而,REBCO超导块材捕获磁场的高低,不仅与其自身特性有关,还与其磁化的方式有关,即与样品在不同条件下的磁化机制密切相关.为了更好的研究高温超导体在不同条件下的磁化机制和磁化规律,进一步提高REBCO超导块材的捕获磁场强度,我们自主设计并制作了一种可实时测量大尺寸REBCO超导块材三维空间磁场及样品表面温度分布的装置.在液氮温度(77K)下,通过对磁化过程中圆柱状单畴GdBCO超导块材表面中心由内到外不同位置处磁场的测量,获得了样品的三维磁场强度随外加磁场实时变化的动态曲线图,揭示了随外加磁场的变化,GdBCO超导块材体内磁场由外向内逐渐扩散和运动、由内向外逐渐扩散和逃逸的机制,同时,对样品中存在的磁通蠕动规律进行了分析.此外,本装置还可用于对其它设备(如电机等)的动态磁场和温度进行实时测量.     

NaNO2晶体线性和非线性光学系数的计算

使用从头计算平面波赝势方法,计算了NaNO₂晶体电子能带结构,并使用改进的倍频公式计算了它的线性折射率和静态二级非线性系数,所得到的结果和实验值相符.采用实空间原子切割方法分析了阳离子和阴离子基团对光学性质的贡献.计算表明(NO₂)-基团对双折射率和倍频系数的贡献占主要地位,从而进一步验证了阴离子基团理论的正确性 关键词： 电子结构 非线性光学系数 从头计算方法     

C60分子电子激发态结构的理论研究

C₆₀分子有较丰富的分子键轨道,同时C₆₀分子离子是稳定存在的,因此预期C₆₀分子的里德伯轨道也是稳定存在的。本文在独立电子近似的基础上,应用多重散射自洽场方法,从理论上统一自洽地探讨了C₆₀分子的分子键轨道和分子里德伯轨道的能级结构。这些轨道能级结构在独立电子近似的层次上模拟了C₆₀分子的电子结构。所得结果和已有的理论和实验结果进行了比较和分析,说明本文结果是自洽合理的,并和已有的实验值符合良好 关键词：     

The determination of low lying ionization potentials of BN,BN+ and B2N and photodetachment energies of BN− and B2N− using the multiconfigurational spin tensor electron propagator method

The multiconfigurational spin tensor electron propagator method (MCSTEP) is a Green's function based approach for directly calculating accurately the low lying ionization potentials (IPs) and electron affinities (EAs) of highly correlated closed and open shell molecules. The MCSTEP method has been employed to determine the vertical ionization potentials and adiabatic ionization potentials of BN, BN⁺ and B₂N and the photodetachment energies (PDEs) of BN^? and B₂N^?. These systems have had wide industrial applications and have recently been the focus of considerable attention. For BN, the lowest few MCSTEP vertical and adiabatic ionization potentials are in good agreement with other theoretical values previously reported. For BN^? the MCSTEP PDEs are in good agreement with the experimental values and previous theoretical results. MCSTEP vertical and adiabatic IPs for BN⁺ differ for some states compared with other previously reported theoretical values. This is believed to be the first time that the vertical and adiabatic IPs of B₂N have been reported. The MCSTEP PDEs of B₂N are in very good agreement with the experimental values.     

Theoretical study of Mn doping effects and O or Zn vacancies on the magnetic properties in wurtzite ZnO

The effects of including the exchange interaction (J) and Hubbard on-site Coulombic interaction (U) on the structural parameters and magnetic moment of Mn-doped ZnO were explored. The calculations were performed with the plane-wave pseudopotential method along with generalized-gradient approximations (GGA). Using the GGA+U + +J method by applying Hubbard corrections U_d to the Zn 3d states and U_p to the O 2p states, the lattice constants were calculated for various reported Hubbard parameters. The difference in the lattice constants between the calculated results and experimental measurements is within 1% for pure ZnO and pure MnO. This study considers three cases: (i) substitution of Mn for Zn, (ii) substitution of Mn for Zn combined with Zn vacancy, and (iii) substitution of Mn for Zn with O vacancy. Results are shown that the system is ferromagnetic (FM) when zinc vacancies are present. For three cases with oxygen vacancies, only one of them is FM. It was also found that the Hubbard U and exchange interaction J improved the calculated results, allowing it to exhibit good agreement properties for Mn-doped ZnO with the experimental data.     

Al-Mg合金熔体快速凝固过程中微观结构演化机理的模拟研究

采用分子动力学方法对Al₅₀Mg₅₀合金熔体的快速凝固过程进行了模拟,并采用双体分布函数、键型指数法和原子团类型指数法等方法,从微观结的不同层面对Al-Mg合金熔体快速凝固过程中微观结构的演化机理进行了深入的分析研究.结果表明：本模拟所获得的Faber-Ziman偏结构因子与实验结果符合较好.Al₅₀Mg₅₀合金熔体具有遗传性,在快速凝固过程形成了非晶态结构,其中二十面体短程序结构对非晶态结构的形成起决定性作用.基于原 关键词： Al-Mg合金熔体 快速凝固过程 分子动力学模拟 微观结构     

Charge density of Ga<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Al<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sb

Charge density calculations and electronic band structures for Ga _x Al_{1 − x} Sb with x = 1.0, 0.5 and 0.0 are presented in this work. The calculations are performed using the empirical pseudopotential method. The charge density is computed for a number of planes, i.e. z = 0.0, 0.125 and 0.25 A ₀ by generating the potential through a number of potential parameters available in the literature. The virtual crystal approximation was applied for the semiconducting alloy. The characteristics of the band structure and charge density are observed to be affected by the potential parameters. Calculated band gaps and the nature of gaps are in good agreement with the experimental data reported. The ionicity is also reasonably in good agreement with other scales proposed in the literature; however the formulation needs to be improved. The present work also demands indirect experimental band gap for the alloy.      

A Study on the Morphology and Mechanical Properties of PVC/nano‐SiO2 Composites

Three methods were used to modify nano‐SiO₂ particles with various interfaces and interfacial interactions between the particles and Poly(vinyl chloride) (PVC) matrix. The experimental results show that direct surface treatment of nano‐SiO₂ particles with a silane coupling agent (KH‐550) is not effective for improving the mechanical properties of PVC/SiO₂ composites. Both ultrasonic oscillations and high energy vibromilling improve the interfacial interactions between SiO₂ particles and PVC matrix. With these methods, the aggregation of SiO₂ particles was inhibited and a good dispersion of SiO₂ particles in PVC matrix was obtained, which improved the mechanical properties of the PVC/SiO₂ composite. The mechanical properties of the PVC/SiO₂ composite with high energy vibromilling modified SiO₂ particles were remarkably improved. Scanning electronic microscopy (SEM), transmission electronic microscopy (TEM), dynamic mechanical analysis (DMA), and theoretical calculations demonstrate these improvements.     

光泵重水气体产生THz激光的半经典理论分析

从半经典密度矩阵理论出发，采用三能级系统模型对光泵重水气体产生太赫兹激光进行了理论分析，求解得到了脉冲光泵重水气体分子产生太赫兹激光过程中激光信号增益系数G_s和抽运光信号被吸收系数G_p的表达式，通过迭代法对太赫兹激光信号的输出光强进行了数值计算，理论计算得到的频谱特性曲线完全符合受激Raman辐射的频谱特性，即频谱宽度较大、输出光强随抽运失谐量的改变而变化明显等特征.在脉冲激光抽运受激Raman辐射过程中，工作介质D₂O气体分子的偶极矩由于受到抽运脉冲光场的扰动发生变化，在频谱特性曲线中表现为受激辐射THz信号的谱线发生了分裂.理论计算结果与已报道的实验结果能较好地相符.     

Improved charge trapping flash device with Al2O3/HfSiO stack as blocking layer

In this paper, we investigate an Al₂O₃/HfSiO stack as the blocking layer of a metal-oxide-nitride-oxide-silicon-type (MONOS) memory capacitor. Compared with a memory capacitor with a single HfSiO layer as the blocking layer or an Al₂O₃/HfO₂ stack as the blocking layer, the sample with the Al₂O₃/HfSiO stack as the blocking layer shows high program/erase (P/E) speed and good data retention characteristics. These improved performances can be explained by energy band engineering. The experimental results demonstrate that the memory device with an Al₂O₃/HfSiO stack as the blocking layer has great potential for further high-performance nonvolatile memory applications.     

Estimation of the ionization potential for polyhalogenated hydrocarbons by weakest bound potential method

The weakest bound potential method was proposed to estimate the ionization potential (IP) of polyhalogenated methanes, that is, the model IP = aχ_ve + bPEI_fi + c was developed, in which χ_ve is molecular electronegativity calculated by valence electrons equilibration method, and polarizability effect index (PEI)_fi is the influence of polarizability effect. The result indicates that the model is reasonable and effective to predict the IP for polyhalogenated methanes. Besides, the quantum chemistry method, the MOPAC AM1 method, and the density functional theory (B3LYP) method were employed to calculate the IP values of the same polyhalogenated methanes, and those results were less than that of the weakest bound potential method. Furthermore, the experimental values of 67 polyhalogenated hydrocarbons were correlated with the parameters χ_ve and PEI_fi. The regression results show a good correlation (R = 0.988), and the average absolute error between the experimental values and the calculated values is only 0.10 eV. Copyright © 2011 John Wiley & Sons, Ltd.