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The dielectric properties of Cu0.5Tl0.5Ba2Ca2?yMgyCu0.5Zn2.5O10?δ (y = 0, 0.5, 1.0, 1.5) superconductor samples were studied at 79 and 290 K by means of capacitance (C) and conductance (G) measurements with the test frequency (f) in the range of 10 KHz to 10 MHz. A negative capacitance (NC) phenomenon has been observed, which is most likely arising due to higher Fermi level of ceramic superconductor samples than metal electrodes. Also the NC may be due to the space charge located at the multiple insulator–superconductor interfaces (grain boundaries) in the materials. The negative dielectric constant (ε′) and loss factor (tan δ) show strong dispersion at low frequencies. The lower thermal agitation at 79 K may enhance the polarizability and hence the dielectric constants (ε′ and ε″).  相似文献   

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A systematic study of the weak link behaviour for (Cu0.5Tl0.5?xKx)Ba2Ca2Cu3O10?δ (x = 0, 0.25) superconductors samples has been carried out using electrical resistivity and AC-susceptibility techniques. The K-doped (Cu0.5Tl0.5?xKx)Ba2Ca2Cu3O10?δ samples were synthesized by solid-state reaction method. In magnetic susceptibility measurements, the real (χ′) and imaginary (χ″) parts of the magnetic susceptibility of (Cu0.5Tl0.5?xKx)Ba2Ca2Cu3O10?δ (x = 0, 0.25) samples were measured as a function of temperature under various DC-magnetic fields up to 172 Oe. It is observed from these studies that the magnitude of the diamagnetism is substantially enhanced by K-doping. The possible reasons for the enhanced magnitude of diamagnetism have been investigated. It is observed from in-field magnetic measurements that the inter-grain coupling is improved with the K-doping. It is concluded from these studies that potassium atoms appearing at the crystal boundaries enhance inter-grain coupling and pinning mechanism in K-doped (Cu0.5Tl0.25K0.25)Ba2Ca2Cu3O10?δ superconductors.  相似文献   

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An intercomparison of Fluctuation Induced Conductivity (FIC) of Cu0.5Tl0.5Ba2Can?1CunO2n+4?y (n = 2, 3, 4) [CuTl-12(n ? 1)n] superconductor thin films is given. We tried to find any correlation between the critical temperature and the parameters extracted from the excess conductivity data i.e. cross-over temperature, pseudogap temperature and fluctuation amplitudes. We found that the critical temperature seems to depend on the fluctuation amplitude; greater the fluctuation amplitude higher is the critical temperature.  相似文献   

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The effect of Er substitution on the mechanical properties of ab- and a(b)c-planes of melt-textured YBa2Cu3O7?δ is reported in the present work. The non-oxygenated samples were characterized by scanning electron microscopy, X-ray diffraction and mechanical properties by instrumented indentation and conventional Vickers indentation whereas the superconducting properties were determined by resistivity measurements on oxygenated samples. The X-ray pattern and EDS analysis revealed the presence of Y-123, Y-211 and BaCeO3 phases. Er substitution up to 5 wt.% did not affect the superconducting properties. No difference in hardness was observed for the ab- and a(b)c-planes. Elastic modulus of the a(b)c-plane was 10% higher than of the ab-plane. Differences in indentation fracture toughness obtained by conventional Vickers indentation of the ab- and a(b)c-planes was observed. The addition of 5 wt.% of Er did not affect significantly the mechanical properties of melt-textured samples when compared with pure melt-textured YBa2Cu3O7?δ.  相似文献   

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The Cu1?xTlxBa2Ca1Cu2O8?δ superconductor thin film samples were bombarded with protons, Si and Au ions of energies 6, 20 and 20 MeV respectively using 5MV tandem pelletron accelerator at Experimental Physics Labs. Each un-irradiated sample had different values of normal state resistivity and the zero resistance critical temperature. The zero resistivity critical temperature has been increased after the irradiation by Si and Au ions. The fluctuation induced conductivity (FIC) analysis of the as-prepared and the ion irradiated samples were performed in the light of Aslamasov–Larkin (AL) theory. The FIC analysis has shown three dimensional (3D) fluctuations in the order parameter in all the samples along with a cross-over to two dimensional (2D) fluctuations at higher temperature. The 3D–2D cross-over temperature has been shifted to higher values after the ion irradiation. Moreover, a direct correlation between the zero resistivity critical temperature, 2D–3D cross-over temperature (TLD) and superconductivity fluctuation temperature (Tscf) was observed. These studies have shown that the fluctuation induced conductivity (excess conductivity) depends on the density of defects and is independent of their nature.  相似文献   

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我们测量了高温超导体 Tl_2Ba_2Ca_2Cu_3O_y 多晶样品的磁化强度弛豫及在小场,高场情形下的磁滞回线,并推出了该样品的钉扎势 U_0 在77K 的温度下随外加磁场的变化关系:当20mT<μ_0H<106mT 时,U_0∝H~(-0.1),当230mT>μ_0H>106mT,U_0∝H~(-0.8).我们认为这是由于随着外场增加,起主要作用的钉扎中心从样品中超导颗粒间钉扎转向超导颗粒内部钉扎.小场下的磁滞回线及扫描电镜形貌相表明该样品具有颗粒性质.  相似文献   

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The objective of this work is to investigate the effect of Ag nanoparticles on critical current of YBa2Cu3O7?δ (YBCO) superconductor. Ag nanoparticles with different particle sizes from 30 to 1000 nm were prepared through the chemical reduction of AgNO3 in an alcohol solution. Then, samples of YBCO superconductors were doped by 1 and 2 wt.% of Ag nanoparticles with different sizes. Samples were characterized with XRD, SEM and EDX measurements. Critical current measurements were performed using a standard four-probe technique at liquid nitrogen temperature. The results showed by increasing of Ag nanoparticles up to 700 nm the Jc increases, but decreases by further increase in Ag particles size. The critical current enhancement is attributed to the improved connectivity between the grain boundaries and better crystallization of the grains.  相似文献   

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The variation of the transverse magnetoresistance of YBa2Cu3O~6.95 high-temperature superconducting ceramic with external magnetic field intensity H ext first increasing from zero to ~500 Oe (Δρ+ / ρ273 K) and then decreasing from about 500 Oe to zero (Δρ? / ρ273 K) is studied for transport current densities varying from j/j c ≈ 0.01 to ≈0.99 (where j c is the critical current density in the absence of the magnetic field) at 77.3 K. It is found that the field dependence of the magnetoresistance of YBa2Cu3O~6.95 high-temperature superconductor is characterized by pronounced hysteresis, the difference Δρ+ / ρ273 K ? Δρ? / ρ273 K increasing with j/j c. As j/j c grows, the effective critical fields of Josephson weak links, H c2J , and the lower critical fields of superconducting grains, H c1A , decline. When field H ext rises, the critical fields are lower than when H ext diminishes: H c2J + < H c2J ? and H c1A + < H c1A ? .  相似文献   

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Two samples of Y1Ba2Cu3O9−δ, one fabricated at Los Alamos National Laboratory and the other at the University of Wuppertal, were tested in the rf field of a niobium cavity at 3 GHz and in a temperature range from 4.2 to 300 K. The data show a sharp reduction of the Joule losses in the samples beginning at an onset temperature of 98 and 92 K, respectively. The residual losses of the sample were measured at 4.2 K where the host cavity was superconducting. The ratio of these losses to the ones observed slightly above Tc was less than 1.1 × 10−2. This indicates that only a small fraction of the conduction electrons of the Y1Ba2Cu3O9-δ sample remain unpaired. The dependence of the rf losses on the rf magnetic field allows the determination of a maximum surface current density which is found to be about 5 × 104 A/cm2.  相似文献   

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测量了 Tl_2Ba_2Ca_2Cu_3O_z 单相超导体在不同外磁场及不同测量频率下的交流磁化率实部和虚部随温度的变化关系,发现实部曲线的起始转变温度 T_(onset)和虚部曲线的峰值温度 T_m,在一定测量频率下都与外磁场的2/3次方成线性关系,在一定外磁场下 T_(onset)与测量频率的对数成线性关系.并且我们认为 T_(onset)和 T_m 都不是一般意义的 T_c,而是受磁通格子熔化影响较大的特殊温度点,所以对 T_(onset)及 T_m 的研究可以反映超导体的磁通格子熔化特性,很值得进一步的研究.  相似文献   

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研究了Tl2Ba2Ca2Cu3Oy大块超导体的磁化和磁通钉扎势。由ZFC磁化测量发现,在远低于Tc的温度发生2D-3D转变。由磁驰豫确定的磁通钉扎势Up与磁场之间遵守Up∝H^-α,且α≈1,在H<Hc1磁场范围内,弱连接超导体的钉扎势则遵守Up∝exp[-H/A]关系,且A=60。  相似文献   

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