Influence of heat treatment on the superconducting properties of Bi1.6Pb0.3Sb0.1Sr2Ca2Cu3O y

Differently heat-treated samples with the nominal composition Bi_1.6Pb_0.3Sb_0.1Sr₂Ca₂Cu₃O _y were studied by resistance and ac susceptibility measurements in the temperature range 77 K<T<200 K. The X-ray diffraction patterns at room temperature were also investigated. The experimental results show that repeated quenchings can depress the formation of the 80 K phase, and enhance the formation of the 110 K phase.     

Femtosecond-excimer-laser patterning of YBa2Cu3O7 films

Projection patterning of Y-Ba-Cu-O films on (100) SrTiO₃ and (100) MgO substrates using femtosecond KrF-excimer-laser pulses is reported     

Transport current density of (Bi1.6Pb0.4)Sr2Ca2Cu3O10 superconductor added with different nano-sized ZnO

The (Bi_1.6Pb_0.4)Sr₂Ca₂Cu₃O₁₀ZnO _x (x=0–0.05 wt%) superconductor with addition of ZnO with average particle size 6 nm and 30 nm was prepared using the co-precipitation method. The ZnO particle size was larger than the coherence length, ξ, and smaller than the penetration depth, λ, of the superconductor. The microstructure, transition temperature (T _c) and transport critical current density (J _c) were studied. SEM micrographs showed a homogeneous distribution of ZnO nanoparticles throughout the samples. J _c of all the ZnO added samples were higher than the non-ZnO added sample. The maximal J _c and T _c were observed when x=0.02 wt% for both series. J _c (77 K) of the 6-nm ZnO added sample was 46 times larger than the non-ZnO added sample. The 6-nm ZnO added sample also showed higher J _c compared to the 30-nm ZnO added sample. ZnO with size closer to ξ was more effective in enhancing J _c.     

Comparative photoemission study of Bi2(Sr,Ca)3Cu2O8+y and Bi1.7Pb0.3Sr2Ca2Cu3O10+y

The electronic structure of Bi-based 2223 single phase superconductor has been studied by ultraviolet and X-ray photoemission. By comparison with that of 2212 phase superconductor, we find a higher density of states nearE _F for 2223 phase. From analysis of the Cu 2p core-level spectroscopy, we obtain a relatively smaller charge transfer energy between copper and oxygen as well as the Coulomb repulsion energy on Cu site for 2223 phase. We relate these changes to the increase of hole concentration from 2212 to 2223 phase. The experimental results support the viewpoint that the transition temperature should be correlated with the density of states atE _F .     

Ultrasonic measurements on polycrystalline YBa2Cu3O7

Temperature dependent ultrasonic attenuation data of polycrystalline YBa₂Cu₃O₇ at 10 MHz show a plateau between 220 and 250 K, and slope changes at 263, 135 and 97 K. The attenuation does not display a sharp decrease at T_c as would be described in the BCS theory. Around 255 K, the sound velocity in the sample increases from its room temperature value by more than 10%.     

Dynamics of optically excited quasiparticles in YBa2Cu3O7

We present a detailed investigation of the dynamics of laser-excited quasiparticles in YBa₂Cu₃O₇ thin films below the critical temperature. Reflectivity transients at low temperature trace the generation and recombination behavior of quasiparticles. The quasiparticle cascading and recombination rates are determined by comparison with a detailed nonlinear model of the quasiparticle dynamics based on extended Rothwarf-Taylor equations.     

Electrical and magnetic properties of variously annealed Bi(Pb)−Sr−Ca−Cu−O thick films

Superconducting thick films with the nominal composition of Bi_1.9Pb_0.4Sr_1.9Ca_2.1Cu_3.2O₁₀ were prepared by the screen-printing method, using an oxalate synthesis for making the paste, and different heat treatments for final samples. A large difference in the structural and superconducting properties between the unmelted and melted samples, and small deviations between the melted and variously annealed specimens were observed. In the first case, the structure is determined by randomly distributed small microcrystals, while in the second, by highly orientated big ones, which results in dissimilar electrical and magnetic features. Therefore the magnetic moment and superconducting material ratio are bigger in the unmelted samples, but in the melted ones, the superconductivity can be characterized by much higher electrical and magnetic parameters. In particular, the transport critical current has conspicuously greater values in the melted as compared to the unmelted samples. In some melted specimens a hyperdiamagnetic signal has been found up to 242 K, induced by the fine details of the preparation technique. The simplest possible reason for this is the diamagnetic Cu–O content in the samples.     

Atomic-level studies of superconducting and nonsuperconducting YBa2Cu3O7−x

Atomic-resolution images from superconducting and nonsuperconducting samples of YBa₂Cu₃O_7–x have been obtained by field ion microscopy. Both phases of the material exhibit a similar layered structure in the field ion images. Transmission electron micrographs of superconducting field ion tips show vividly the twinned structure of the orthorhombic phase. Time-of-flight (atom-probe) mass spectra from the two materials differ primarily in an enhanced molecular oxygen signal from the superconducting samples indicating that oxygen in the O(4) sites (CuO chains) is field desorbed preferentially as molecular oxygen ions.     

Step-like growth of Bi2Sr2CaCu2O8 films on off axis oriented (001) SrTiO3

High-quality Bi₂Sr₂CaCu₂O₈ (BSCCO) films were grown by means of pulsed-laser deposition on 10° off-axis oriented (001) SrTiO₃ substrates. The films exhibit a step-like morphology and they are properly oriented along the (001) direction. Their normal-state resistivity measured along the tilt (off-axis (100) direction of the substrate) was, typically, 260 times higher than that along the (010) direction. Such films reveal a transverse Seebeck-effect which significantly exceeds that observed with YBa₂Cu₃O₇ (YBCO).