YBa2-xSrxCu3O7-δ系统的超导电性与结构的关联

本文系统地研究了YBa_2-xSr_xCu₃O_7-δ中超导电性与物相以及结构变化之间的关系。发现当0c并不随Sr的含量而单调变化。在x=1.0处,T_c出现一峰值。同时,超导临界温度与样品的晶体结构之间呈现出强烈的相关性:随着正交性的增强(即a,b间差值的增大),T_c单调地上升。本文还就S 关键词：     

在H2气氛中Bi2Sr2CaCu2O8+δ的热处理效应

对高品质单相多晶Bi₂Sr₂CaCu₂O_8+δ样品作真空或H₂气氛中不同温度下的热处理。由X射线结构分析,其正常态和超导态性质(特别是载流子浓度)的系统测量结果表明:Bi₂Sr₂CaCu₂0_8+δ样品在H₂气氛中热处理,其氧的释放可分为两个阶段:一是Bi-O层之间的过量氧原子的逸出,降低系统的载流子浓度,从而调节T_c;二是CuO₂面内氧原子的迁移,产生氧空位,使CuO₂面内Cu²⁺的短程二维反铁磁(2D-AFM)有序背景遭到破坏。可以认为:以往文献中报道的Bi₂Sr₂CaCu₂O_8+δ超导体的吸氢效应导致T_c的变化,很可能主要的并不是氢原子的电子掺杂行为,而是与吸氢过程中氧含量的变化相联系。 关键词：     

YBa2Cu1-xCox(Cu1-yZny)2Oz体系的Co,Zn共同掺杂效应

本文报道通过对YBa₂Cu_1-xCo_x(Cu_1-yZn_y)₂O_z(0≤x,y≤0.1)体系晶体结构、氧含量、正常态电阻-温度关系、Hall效应以及超导临界温度等的综合测量,发现随着Co和Zn含量的增加,体系经历了从正交结构的超导金属向四方结构的非超导半导体的转变,超导临界温度T_c和载流子浓度n_h均迅速下降,Co 关键词：     

反应扩散法制备的PbMo6S8超导带的超导特性

本文报道反应扩散法制备Chevrel相PbMo₆S₈超导带材的过程以及带材的超导特性。Mo带与H₂S气体反应生成单相的Mo-S化合物(MoS₂或Mo₂S₃,根据反应温度而定),再与Pb的蒸汽反应生成单相的PbMo₆S₈薄层。PbMo₆S₈超导层的临界温度T_c=13.0 关键词：     

非晶态超导合金Zr87.7Si12.3中结构弛豫和结晶化对超导

对非易态超导合金Zr_87.7Si_12.3,在适当的温度下进行了lh等时退火处理.测量了其结构、超导临界参量T_c,H_(C2)及其转变宽度ΔT_c,ΔH_c2等的变化.发现些与金属-金属型非晶态合金不同的变化规律,并结合在结构弛豫过程中所发生的拓扑短程有序化和化学短程有序化,以及相应的结晶化机制,对实验结果作了讨论. 关键词：     

MgB2 超薄膜的制备和性质研究

利用混合物理化学气相沉积法在6H-SiC(001)衬底上制备干净的MgB₂超导超薄膜.在本底气体压强、载气氢气流量等条件一定的情况下,改变B₂H₆流量及沉积时间,制备得到不同厚度的系列MgB₂超薄膜样品,并研究了超导转变温度T_c、剩余电阻率ρ_(42K)、上临界磁场H_c2等与膜厚的关系.该系列超薄膜沿c轴外延生长,随膜厚度的变小,T_c(0)降低,ρ_(42K)升高.膜在衬底上的生长遵循Volmer-Weber岛状生长模式.对于厚度为7.5 nm的MgB₂超薄膜,T_c(0) =32.8 K,ρ_(42K) =118 μΩcm,是迄今为止所观测到的厚度为7.5 nm的MgB₂超薄膜最高的T_c值;对于厚度为10 nm的MgB₂膜,T_c(0)=35.5 K,ρ_(42K)=17.7 μΩcm,上临界磁场μ₀H_c2估算为12 T左右,零磁场、4 K时的临界电流密度J_c=1.0×10⁷ A/cm²,是迄今为止10 nm厚MgB₂超薄膜的最高J_c值,且其表面连接性良好,均方根粗糙度为0.731 nm.这预示MgB₂超薄膜在超导纳米器件上具有广阔的应用前景. 关键词： 2超薄膜')" href="#">MgB₂超薄膜 薄膜生长 氢气流量 混合物理化学气相沉积     

Ta对C—15相V2Hf和V2(Zr0.5Hf0.5)系列声子性能的影响

本文用中子飞行时间方法对C-15相的超导材料V₂Hf,V₂Ta和V₂Hf_0.8Ta_0.2以及V₂Zr_0.5。Hf_0.5和V₂Zr_0.5Hf_0.33Ta_0.17的热中子非弹性散射谱作了测量,并计算出相对的广义声子态密度。结果与早先发表的Nb对C-15相V₂Zr和V₂(Hf_0.5Zr_0.5)系列声子性能的影响一致:声子频率随超导转变温度T_c增加而软化,随T_c减小而硬化。这表明,对于此类材料弹性软化在一定程度上对提高T_c起了作用。结果还进一步表明V₂Zr或V₂Hf与V₂(Zr_0.5Hf_0.5)之间有着质的差别,V₂Hf加Ta后,T_c增加,声子频率软化,而V₂(Zr_0.5Hf_0.5)加Ta后,T_c减小,声子频率则略有硬化。这与V₂Zr和V₂(Hf_0.5Zr_0.5)加Nb的结果是一致的。此结果可以用角动量分波表象的能带论方法分析电-声耦合相互作用得出的杂化理论来定性解释。 关键词：     

YBa2(Cu0.95M0.05)3O7-δ的代换效应及其中子衍射研究

X射线衍射实验表明YBa₂(Cu_0.95M_0.05)₃O_7-δ(M=Ti,V,Cr,Mn,Fe,Co,Ni,Cu和Zn)均为单相结构。Fe,Co,Ni和Zn对Cu的替代使超导临界温度T_c显著下降,而同样含量的Ti,V,Cr,Mn对Cu的替代并未对超导性能产生显著影响。并利用中子衍射分析了Ti,Mn,Fe和Co对Cu原子的取代,发现代换原子对Cu的两个晶位各自存在不同的择优占据 关键词：     

块体金属玻璃Zr46.75Ti8.25Cu7.5Ni10Be27.5的超导与负电阻温度系数

测量了块体金属玻璃Zr_46.75Ti_8.25Cu_7.5Ni₁₀Be_27.5在退火前后其电阻值随温度的变化,测量的温度范围为1.5—300K.样品在退火前后都发现有超导现象.零磁场下其超导转变温度T_c分别为1.84和3.76K.在5—300K温度范围内,原始样品具有负的电阻温度系数.如果取Zr, Ti, Cu, Ni及Be分别贡献出1.5, 1.5, 0.5, 0.5及两个传导 关键词： 块体金属玻璃 超导 电阻温度系数     

C-15结构(Hf,Zr,Ta)V2和(Hf,Zr,Nb)V2合金超导转变的压力效应研究

本文研究了C-15结构化合物(Zr_0.5Hf_0.5-xTa_x)V₂(x≤0.2)和(Hf_0.5Zr_0.5-xNb_x)V₂(x≤0.2)的超导转变温度T_c及其压力效应?T_c/?P。报道了实验方法与结果。与(Hf_1-xTa_x)V₂和(Zr_1-xTa_x)V₂的情况不同,在(Zr_0.5Hf_0.5-xTa_x)V₂中Ta的引入使常压下的T_c下降,然而(?)T_c/(?)P却大为提高。因此高压下Zr_0.5Hf_0.45Ta_0.05V₂的T_c反而比Hf_0.5Zr_0.5V₂更高。导出了一个基于角动量分波表象能带论方法的描述压力效应的新关系式。它指出导带电子波函数中的高角动量成分变化对T_c的压力效应影响比较重要。这个公式有助于理解上述复杂的实验现象,并能合理地解释某些元素(如Cs,Ba,La等)的T_c随压力剧增的事实。 关键词：     

掺Ba对Bi系2212相超导电性的影响

研究了掺Ｂａ对Bi₂Sr_2-xBa_xCaCu₂O_y（０≤ｘ≤０．１５，０．３）单晶和多晶样品超导电性的影响，结果表明，有少量Ｂａ^２＋离子进入了超导相，且有固溶度极限．对于２２１２相单晶，ｃ轴参数和Ｔ_c均随Ｂａ含量增加而增加；对于慢冷多晶样品，掺Ｂａ可明显提高Ｔ_c；然而对于淬大多晶样品，Ｔ_c没有明显变化，用掺Ｂａ 关键词：     

Superconductivity in CeCu2Si2

Resistivity measurements of CeCu₂Si₂ are carried out under pressures p up to 12 kbars. Unlike polycrystalline samples, no traces of superconductivity have been observed in CeCu₂Si₂ at ambient pressure. When pressure is applied, CeCu₂Si₂ monocrystals become superconducting with anomalously large ratio H_c2(0)/T_c (0) = 34 K0e/K and with the derivative dH_c2/dT(T=T_c) = 140 K0e/K     

Vortex lattice in Bi2Sr2CaCu2O8+δ well above the first-order phase-transition boundary

Measurements of non-local in-plane resistance originating from transverse vortex-vortex correlations have been performed on a Bi₂Sr₂CaCu₂O_8+δ high-T_c superconductor in a magnetic field up to 9 T applied along the crystal c-axis. Our results demonstrate that a rigid vortex lattice does exist over a broad portion of the magnetic field-temperature (H-T) phase diagram, well above the first-order transition (FOT) boundary H_FOT(T). The results also provide evidence for the vortex lattice melting and vortex liquid decoupling phase transitions, occurring above the H_FOT(T).     

Neutron diffraction determination of the magnetic phases of CoCl2·2H2O

The metamagnetic behaviour of CoCl₂·2H₂O has been determined by means of neutron diffraction. At T = 4.2 K the reflections of the antiferromagnetic zero-field phase disappear, when a magnetic field of H_c1 = 31.8 kOe is applied along the b axis. The new ferrimagnetic phase vanishes at H_c2 = 46.1 kOe and the magnetically saturated configuration is reached. The three phases meet at a triple point at T_T = 8.9 K and H_T = 37.5 kOe. Two types of phase transition have been detected.     

The heat capacity of the layer compounds (CH3CH2CH2NH3)2MnCl4 and (CH3CH2CH2NH3)2CdCl4 from 10 K TO 300 K

The heat capacity of the layer compounds tetrachlorobis (n-propylammonium) manganese II and tetrachlorobis (n-propylammonium) cadmium II, (CH₃CH₂CH₂NH₃)₂MnCl₄ and (CH₃CH₂CH₂NH₃)₂CdCl₄ respectively, has been measured over the temperature range 10 K ?T ? 300 K.Two known structural phase transitions were observed for the Mn compound in this temperature region: at T = 112.8 ± 0.1 K (ΔH_t= 586 ± 2 J mol^?1; ΔS_t = 5.47 ± 0.02 J K^?1mol^?1) and at T =164.3 ± (ΔH_t = 496 ± 7 J mol^?1; ΔS_t =3.29 ± 0.05 J K^?1mol^?1). The lower transition is known to be from a monoclinic structure to a tetragonal structure, while the upper is from the tetragonal phase to an orthorhombic one. From comparison with the results for the corresponding methyl Mn compound it is deduced that the lower transition primarily involves changes in H-bonding while the upper transition involves motion in the propyl chain.A new structural phase transition was observed in the Cd compound at T= 105.5 ± 0.1 K (ΔH_t= 1472.3 ± 0.1 J mol^?1; ΔS_t = 13.956 ± 0.001 J K^?1mol^?1), in addition to two transitions that have been observed previously by other techniques. The higher of these transitions(T = 178.7 ± 0.3 K; ΔH_t = 982 ± 4 J mol^?1 ΔS_t = 6.16 ± 0.02 J K^? mol^?1) is known to be between two orthorhombic structures, while the structural changes at the lower transition (T= 156.8 ± 0.2 K; ΔH_t = 598 ± 5 J mol^?1, ΔS_t = 3.85 ± 0.03 J K^?1 mol^?1) and at the new transition are not known. It is proposed that these two transitions correspond respectively to the tetragonal to orthorhombic and monoclinic to tetragonal transitions in the propyl Mn compounds.In addition to the structural phase transitions (CH₃CH₂CH₂NH₃)₂MnCl₄ magnetically orders at t? 130 K. The magnetic contribution to the heat capacity is deduced from the heat capacity of the corresponding diamagnetic Cd compound and is of the form expected for a quasi 2-dimensional Heisenberg antiferromagnet.     

Relationship between chemical bond parameters and superconducting temperature in HgBa2Can−1CunO2n+2+δ (n=1, 2, 3, 4)

Bond covalency and valence of elements in HgBa₂Ca_n−1Cu_nO_2n+2+δ (n=1, 2, 3, 4) were calculated and their relationship with T_c was discussed. For both oxygen and argon annealed samples, the results indicated that with the increase of n, the trend of bond covalency of Hg-O and Cu-O was the same or opposite compared with that of superconducting temperature. This may suggest that the magnitudes of Cu-O and Hg-O bond covalency are important in governing the superconducting temperature. For the highest T_c sample, Hg had the lowest valence, implying that lower valence of Hg was preferred in order to produce higher T_c. For fixed n, the valence of Cu in oxygen annealed samples was larger than that in argon annealed samples, indicating that oxygen annealed samples produced more carriers than argon annealed samples.     

Superconductivity of powder-in-tube Sr0.6K0.4Fe2As2 wires

Nb-sheathed Sr_0.6K_0.4Fe₂As₂ superconducting wires have been fabricated using the powder-in-tube (PIT) method for the first time and the superconducting properties of the wires have been investigated. The transition temperature (T_c) of the Sr_0.6K_0.4Fe₂As₂ wires is confirmed to be as high as 35.3 K. Most importantly, Sr_0.6K_0.4Fe₂As₂ wires exhibit a very weak J_c-field dependence behavior even the temperature is very close to T_c. The upper critical field H_c2(0) value can exceed 140 T, surpassing those of MgB₂ and all the low temperature superconductors. Such high H_c2 and superior J_c-field performance make the 122 phase SrKFeAs wire conductors a powerful competitor potentially useful in very high field applications.