Sansheng WANG
,
Lin WANG
,
Bingfu GU
,
null
材料科学技术（英）
A full solution method has been developed as a low cost process of YBa2Cu3O7-x (YBCO) coated conductor fabrication. In this study, highly biaxially textured SrTiO3 (STO) buffer layers were fabricated on LaAlO3 (LAO) single crystal substrates by sol-gel method using metal alkoxides as the staring precursor materials. High quality YBCO superconducting film was then fabricated on STO-buffered LAO substrate by trifluoroacetic metalorganic deposition (TFA-MOD) method. For the YBCO superconducting film, only (00l) diffraction peaks can be detected by XRD (X-ray diffraction) analysis with no other phases detectable. Especially, In-plane texture of YBCO film is improved compared to that of STO buffer layer from phi scans analysis, which indicates the self-epitaxy phenomenon explained by considering interfacial energy. STO and YBCO films both
show c-axis oriented grains growth and have uniform surface microstructure. A critical transition temperature, Tc (R=0) of 89.5 K and a critical current density of 2 mA/cm2 (77 K, self-field) were obtained for a 0.2 μm thick YBCO film on STO-buffered LAO substrate. No reaction between YBCO and STO was detected by XRD analysis. This full solution process may provide a promising low cost fabrication route for YBCO coated conductors on metal tape.
关键词:
YBCO coated conductor
,
null
,
null
,
null
Li CHEN
,
Hua LI
,
Liangmo MEI
材料科学技术（英）
The electronic structures of new superconducting perovskite MgCNi3 and related compounds MgCNi2T (T=Co, Fe, and Cu) have been studied using MS-Xα method. In MgCNi3, the main peak of density of states is located below the Fermi level and dominated by Ni d. From the results of total energy calculations, it was found that the number of Ni valence electron decreases faster for the Fe-doped case than that for the Co-doped case. The valence state of Ni changes from +1.43 in MgCNi2Co to +3.02 in MgCNi2Fe. It was confirmed that Co and Fe dopants in MgCNi3 behave as a source of d-band holes and the suppression of superconductivity occurs faster for the Fe-doped case than that for the Co-doped case. In order to explain the fact that Co and Fe dopants in MgCNi3 behave as a source of d-band holes rather than magnetic scattering centers that quench superconductivity, we have also investigated the effects of electron (Cu) doping on the superconductivity and found that both electron (Cu) doping and hole (Co, Fe) doping quench superconductivity exist. Comparing with the hole (Co) doping, there was no much difference between Cu and Co doping. This suggests that Co and Fe doping do not act as magnetic impurity.
关键词:
Electronic structure
,
null
,
null
杨大威
,
张小兰
,
杨素华
,
李平原
,
张芸
,
陈永亮
,
张勇
,
潘熙峰
,
闫果
低温物理学报
采用机械合金化法制备了一系列的Nb3Al1-xSix(x=0～0.2)多晶样品,利用高能球磨机获得Nb(Al,Si)固溶体,然后在900℃的温度下烧结将固溶体转变为超导相.XRD测试结果表明,经3小时高能球磨后Al和Si固溶到Nb中形成Nb(Al,Si)固溶体,烧结后的样品具有较好的单相性,为A15型晶体结构,并且晶格随掺杂量的增加逐渐减小.磁性测量结果表明,纯样Nb3Al的Tc约为14 K,随掺Si量的增加Tc逐渐减小.结合EDX分析,所有Nb3Al1-xSix样品的超导电性来源于A15相,但由于随掺杂量的增加样品中Al的含量逐渐减少导致了Tc逐渐减小.
关键词:
Nb3Al超导体
,
超导电性
张小兰
,
杨大威
,
杨素华
,
刘钊
,
李平原
,
张芸
,
陈永亮
,
张勇
,
潘熙峰
低温物理学报
利用高能球磨法制备Nb3Al超导体,先通过高能球磨法获得Nb(Al)固溶体,然后在不超过1000℃的温度下烧结将Nb(Al)固溶体转变为Nb3Al超导相,对其成相反应过程展开研究.研究发现高能球磨法能够获得Nb(Al)固溶体,球磨3小时为宜,时间较短不能完全形成固溶体,时间较长使原料粉末非晶化.在烧结过程中,研究了原料组分、烧结温度及时间对制得超导相性能的影响,最终获得初始原料的化学计量比为Nb:Al=74:26、烧结温度为900℃、烧结时间为1小时制得的Nb3Al超导体的Tc最高,达到15.6K.由于Nb3Al相中的Al含量偏低,导致其Tc偏低.
关键词:
Nb3Al超导体
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超导电性
张明发
,
孙爱民
,
马书懿
,
王丹
,
石盼盼
低温物理学报
本文采用固相反应方法制备了一系列YBa2Cu3O7-δ (Y123)+0.25 molY2O3 +x wt％ BaCeO (x=0.0,2.0,5.0,10.0 and 20.0)多晶样品,通过X射线衍射法(XRD)和扫描电子显微镜(SEM)对Y2O3和BaCeO3的参杂的样品微观结构和超导转变温度进行系统的测量,发现Y2O3参杂到YBCO样品表面有球形或椭球形Y2Ba1Cu1O7-δ(Y211)粒子形成.依据SEM,XRD和电阻率测量,随着BaCeO3参杂量的增加,我们观察到样品的形貌变得越来越不均匀,所有样品的晶体结构有从正交相向四方相转变的趋势,超导转变温度呈金属状态到半导体状态转变的趋势,并伴有三步转变过程;同时也观察到了超导转变温度降低且转变宽度增加的现象,这些结果可以用氧分布的变化和缺陷的变化及氧缺陷来解释.
关键词:
YBa2Cu3O7-δ超导体
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BaCeO3添加
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微观结构
,
超导电性
王广涛
,
张会平
,
张林
,
刘畅
低温物理学报
采用第一性原理计算,我们对BaTi2Bi2O材料的电子结构和磁性做了详细的研究.其非磁性态的计算结果显示,费米能级处的态密度主要来自dz2,dx2-y2和dxy三个轨道的电子.费米面主要有三部分组成,并且将其沿着矢量q1=(π/a,0,0)和q2=(0,π/a,0)平移时,第三部分费米面(沿着X-R连线)与第一部分费米面(M-A连线)嵌套明显,计算得出磁化系数x0(q)在X点出现峰值,这一点与峰值出现在M点的FeAs基超导体不同.上述磁化率峰值可以诱导产生自旋密度波,这使得BaTi2Bi2O的磁性基态是能量基本简并的bi-collinear antiferromagnetism(AF3)与blocked checkerboard antiferromagnetism (AF4)磁性态.随着空穴掺杂,x0(q)的峰值降低并且变得有些不对称,而电子掺杂则导致峰值变大.一般认为超导序和磁性序相互竞争,当自旋涨落被完全压制时,超导出现,这正好可以解释为什么超导只能出现在空穴掺杂型化合物而非电子掺杂型里.
关键词:
第一原理计算
,
费米面嵌套
,
超导
陈羽
,
黄新民
低温物理学报
Cooper考虑一对电子在一个安稳的费米球面上相互作用着，指出这种相互作用是由声子和屏蔽库仑场导致的，在电子间存在一种净的吸引作用，结果这对电子能够形成一个束缚态．我们给出的是对于元素之中有化学键的形成，甚至电了发生了转移，电负性高的元素得到了电子，电负性低的元素失去了电子时退化费米气体中的束缚电子对的描述．
关键词:
Cooper对
,
化学成键
,
超导电性
鲁彦忠
,
孙爱民
,
刘恒伟
,
马耀通
,
马金元
,
艾小倩
,
张永福
,
孙丽娜
,
赵懂叶
,
马书懿
低温物理学报
本文采用固相反应法成功制备出一系列Y123与Y211的摩尔比为1：x（x=0、0．14、0．27、0．3、0．35、0．4、0．45、0．47、0．5、0．8、1．18）的样品．实验结果表明：在0．35≤x≤0．5范围内，Y123的起始转变温度Tonset临界转变温度Tc以及转变宽度△Tc都在x=0．47出现了拐点，这说明了x=0．47为最佳掺杂比例，本文同时也简单阐述了Y123的晶格结构是如何改变其超导电性的．
关键词:
高温超导材料
,
掺杂
,
超导电性
