磁性Gd3+离子对Chevrel相超导体PbMo6S8的临界电流和输运性质的影响

采用高温固态反应和均衡热压方法相结合,我们制备了一系列Gd掺杂的Chevrel相GdxPb1-xMo6S8超导样品.为了研究掺入的磁性Gd3+离子对于磁通线的钉扎作用和对临界电流及其它性质的影响,我们系统地测量了样品的电阻率,热电势,比热和临界电流密度.同时,我们计算了磁性Gd3+离子与磁通线之间的相互作用和这种作用可能导致的磁通钉扎及对临界电流的影响,并与实验结果进行了比较.结果显示除非Gd3+离子的分布是非常不均匀的,Gd3+离子所引起的钉扎是不重要的.另一方面,热电势和电阻率等输运性质及比热的结果显示由于Gd3+取代了Pb2+使载流子浓度降低了.载流子浓度的降低进而引起其它超导参数如热力学临界场Bc的变化,导致钉扎势的减小,最终降低了临界电流.     

Ti-Pd系超导电性的研究

本文给出了Ti-Pd系超导转变温度随合金成份的变化规律,指出Ti-Pd系中超导性是Pd在α-Ti中的固溶体所贡献的,结合这个合金系的相图,讨论了这些结果,认为Pd在α-Ti中的极限固溶度应有较高的数值。 关键词：     

室温快离子导体Rb4Cu16I7Cl13的电导率和热容研究

在-170-100℃的温度范围内,研究了室温快离子导体Rb₄Cu₁₆I₇Cl₁₃的电导率和热容随温度的变化,结果表明该材料在-50℃和-107℃附近各有一个二级相变存在。 关键词：     

La掺杂Bi-2201单晶中宏观相分离迹象的发现及研究

在对系列Ｌａ 掺杂的Ｂｉ２Ｓｒ２ － ｘＬａｘＣｕＯ６ ＋ δ单晶的研究中,我们发现在极度Ｌａ 掺杂（ 空穴极度欠掺杂） 的样品中有高达３６Ｋ 的超导相出现．Ｘ 射线衍射图（ＸＲＤ） 和电镜照片都表明这种极度空穴欠掺的样品有很好的单相性,从而排除了样品化学不纯的可能．另外,对这种样品进行脱氧处理后,此超导电性相应消失,说明了这种高Ｔｃ 的超导电性是由活动性空穴掺杂引起的．虽然对相应样品在正常态的磁测量没有测出反铁磁峰（Ｎｅｅｌ 峰） ,但对系列样品的拉曼散射研究发现样品随着Ｌａ 含量的增多,其反铁磁交换作用明显加强．所以,我们认为这种高Ｔｃ 超导电性的出现是在Ｂｉ２２０１ 体系中存在宏观相分离的明显迹象     

PHASE SEPARATION AND JOSEPHSON-COUPLING ORIGIN FOR THE ANOMALOUS Hc2 BEHAVIOR IN OVERDOPED Bi2Sr2-xLaxCuO6+δ CRYSTALS

Hole-overdoped Bi₂Sr_2-xLa_xCuO_6+δ single crystals with two coexistent superconducting transitions have been intensively studied by measuring the dc magnetic susceptibility. It is found that the coexistence of these two phases cannot be attributed to any chemical or vortex dynamical effect but to some intrinsic driving force, such as the electronic-driven phase separation. Furthermore, the upper critical fields of the two phases behave in a rather different way; that is, one of them shows a "normal H_c2 behavior" which can be described by the critical fluctuation theory, while the other exhibits an "anomalous H_c2 behavior" and can be well explained by a recent theory based on an assumption of a Josephson-coupling origin, indicating a strong evidence of Josephson-coupling origin for the upward curvature of the so-called H_c2 in high T_c superconductors.     

WEAK QUANTUM FLUX CREEP AND STRONG PINNING IN THE NEW SUPERCONDUCTOR MgB2

The newly discovered superconductor MgB₂ has a transition temperature T_c of about 40 K, which is touching the upper line of that predicted by the phonon-mediated Bardeen--Cooper--Schrieffer (BCS) theory. It is interesting to investigate the flux creep in MgB₂ and compare it with other superconductors. We have measured the magnetization relaxation of MgB₂ sintered at high temperature and high pressure. It is found that the quantum tunnelling and the thermally activated flux creep are very weak, implying a strong pinning in this material.     

顺磁性对单晶GdBa_2Cu_3O_（6＋y）临界电流密度的影响

由于单晶ＤｄＢａ２Ｃｕ３Ｏ６＋ｙ样品中Ｇｄ３＋离子本身固有的磁矩对样品有顺磁贡献，使得样品的磁滞回线有所倾斜并使磁滞回线的宽度增大，因而使根据Ｂｅａｕ模型得到的临界电流密度偏离了其真正的值．在温度Ｔ＝４．２Ｋ时，偏离达到８％．因而在对ＹＭＯ和ＧＢＣＯ进行比较研究时，对ＧＢＣＯ临界电流密度的修正是必要的．这一顺磁磁化强度的磁场依赖关系可以用反铁磁的分子场理论给以很好的描述．     

TI结构Na_(0.33)WO_3的电阻率随温度变化反常

为研究NaxWO3系统的反常超导性质,我们以分析纯Na2WO4和WO3为原料,用熔盐电解法制备了几种组分的钠钨青铜单晶样品.其中发现Na0.33WO3的电阻率随温度的变化关系反常. Na0.33WO3的制备过程如下:将Na2WO4和WO3分别占40%和60%摩尔的原料盛入刚玉坩埚内,加热到780℃,待熔融后进行电     

PHASE SEPARATION AND JOSEPHSON-COUPLING ORIGIN FOR THE ANOMALOUS Hc2 BEHAVIOR IN OVERDOPED Bi2Sr2-xLaxCuO6+δ CRYSTALS

Hole-overdoped Bi₂Sr_2-xLa_xCuO_6+$\delta$ single crystals with two coexistent superconducting transitions have been intensively studied by measuring the dc magnetic susceptibility. It is found that the coexistence of these two phases cannot be attributed to any chemical or vortex dynamical effect but to some intrinsic driving force, such as the electronic-driven phase separation. Furthermore, the upper critical fields of the two phases behave in a rather different way; that is, one of them shows a "normal H_c2 behavior" which can be described by the critical fluctuation theory, while the other exhibits an "anomalous H_c2 behavior" and can be well explained by a recent theory based on an assumption of a Josephson-coupling origin, indicating a strong evidence of Josephson-coupling origin for the upward curvature of the so-called H_c2 in high T_c superconductors.     

掺Ca-(RPr)-123系列超导体的高压合成

利用高温高压方法成功地合成出(R_0.4Pr_0.6)_0.5Ca_0.5Ba₂Cu₃O_7-δ(其中R=La,Pr,Nd,Sm,Eu,Gd,Y)单相123相超导体.其结果表明,在Pr系的R-123相化合物中掺Ca都能够获得高T_c的超导体,其超导转变温度都在100K左右. 关键词： 超导体 Pr-123相化合物 高压合成 稀土