Remanent fields and critical currents in Tl2 Ba2Ca2Cu3Ox ceramic

The temperature and magnetic-field dependences of the remanent magnetization have been determined from far-field measurements for thallium ceramic samples. The current flow that gives rise to the observed magnetization is intragranular. The results are consistent with flux-creep-controlled transport with a distance between pinning centers of - 1/2/m. Using near-field measurements, the superconducting properties are found to be heterogeneous on a scale of 1 mm. Magnetic domains have been induced by pplying spatial variation in the applied field.     

Anisotropic fluctuation magnetoconductivity in Bi2Sr2Ca2Cu3Ox thin films

Measurements of the fluctuation magnetoconductivity as a function of both the magnetic field up to 13 T and the temperature in thin films of Bi₂Sr₂Ca₂Cu₃O_x are presented. The variation of the magnetoconductivity with the magnetic field strength is quadratic at temperatures distantly above the critical temperatureT _c and changes to an entirely negative curvature nearT _c . The latter behavior is attributed to an inhomogeneous critical temperature in the films. The results are analyzed in terms of recent theoretical models for fluctuation-enhanced magnetoconductivity in layered superconductors. The magnetoconductivity in a magnetic field oriented normal to the copper-oxide layers is dominated by the orbital contribution of the Aslamazov-Larkin effect. The magnetoconductivity in the parallel orientation is distinctly smaller and provides evidence for the corresponding Zeeman contribution. The latter measurement also indicates that the Maki-Thompson process may be insignificant in Bi₂Sr₂Ca₂Cu₃O_x.     

A new 1223-type high Tc cuprate (Tl,V) Sr2Ca2Cu3O9

A new 1223-type (Tl, V)-based superconducting layered cuprate (Tl_1–x V _x ) Sr₂Ca₂Cu₃O₉ withx=0.25 and 0.50 has been successfully synthesized in the nearly-pure form and identified by powder X-ray diffration analyses. An excessive quantity of Tl is necessary for the preparation of the (Tl, V)-based 1223-type compound. Resistance and ac susceptibility measurements showed that the new (Tl, V)-based 1223 cuprate exhibits T_c above 110 K.     

Oxygen dependence of the fermi-level and electron-phonon coupling constant in YBa2Cu3Ox films

We present a detailed investigation of the dynamics of laser-excited carriers in YBa₂Cu₃O_x thin films with various oxygen contents x. We observe a Fermi level shift due to oxygen reduction and determine the energy gap between the Fermi level and the upper Hubbard band. The electron-phonon coupling constant is determined as a function of transition temperature.     

Thermoelectric power of YBa2Cu3Ox in equilibrium with gas phases

Thermoelectric power (TP) and electrical conductivity (EC) measurements were performed for YEa₂Cu₃O_x at 1128 K under controlled oxygen partial pressure varying between 50 and 10⁵ Pa. Three regimes are observed for the electrical properties. At low both TP and EC remain constant with . In the medium range sharp changes of both electrical parameters occur; TP changes sign from positive above 4×10² Pa to negative below this value. In the high region (>7.6×10³ Pa) TP vs log exhibits two slopes; 5.1 below 1.5×10⁴ Pa and 8.4 above this value. The slopes can be discussed in terms of the defect structure involving singly and doubly ionized oxygen vacancies below and above 7.6×10³ Pa, respectively.     

Weak link problem and intragrain current density in polycrystalline Bi1Ca1Sr1Cu2Ox and Tl2Ca2Ba2Cu3O10

Polycrystalline sintered specimen were investigated by means of ac susceptibility and inductive critical current measurements. Main objects are whether the new highT _c oxides have a weakly coupled intergranular structure and to get information about the intragrain critical current density. The Tl₂Ca₂Ba₂Cu₃O₁₀ specimen shows a connective nature similar to YBa₂Cu₃O₇ with low intergrain currents (100 A/cm² at 100K,B=0 T) and high intragrain ones (4.5·10⁵ A/cm² at 100K,B=0 T). The investigation of the Bi₁Ca₁Sr₁Cu₂O_x specimen becomes complex due to the presence of two superconducting phases and the low intragrain critical current density of the lowerT _c phase.     

Electron tunneling into thin films of Y1Ba2Cu3O7

We have fabricated tunnel junctions on thin films of Y₁Ba₂Cu₃O₇ which were epitaxially grown by magnetron sputtering on (100) and on (110) oriented SrTiO₃ substrates. These junctions of the type Y₁Ba₂Cu₃O₇/barrier/Pb or In showed with high reproducibility in the conductance a gap-like structure with the maxima near±16mV. We supplied experimental arguments that this structure reflects properties of the quasi particle excitation spectrum of Y₁Ba₂Cu₃O₇. The gap-like structure was found to disappear atT _c mainly by weakening and not by a shift of the peaks to lower voltages.     

Superconducting screen printed thick films of YBa2Cu3O7 and Bi1.6Pb0.4Sr1.6Ca2.4Cu3O10 on polycrystalline substrates

Thick films of YBa₂Cu₃O₇ and Bi_1.6Pb_0.4Sr_1.6Ca_2.4Cu₂O₁₀ have been prepared using a screen printing method on polycrystalline substrates. The films have been characterized by X-ray diffraction, electrical measurements and SEM observations. YBa₂Cu₃O₇ films exhibited T_c ranging from 80 to 87 K on Y₂BaCuO₅ substrates while Bi_1.6Pb_0.5Sr_1.6Ca_2.4Cu₃O₁₀ films on polycrystalline MgO reached the zero resistance state at 104 K with critical current densities of up to 10 A/cm² at 77 K.     

Infrared reflectance spectra and optical conductivity of Tl2CaBa2Cu2O8 and Tl2Ca2Ba2Cu3O10 superconducting thin film samples

Films of the Tl₂CaBa₂Cu₂O₈ (Tl2122 phase) and Tl₂Ca₂Ba₂Cu₃O₁₀ (Tl2223 phase) superconductors were prepared by d.c. magnetron sputtering method. Their C-axes were perpendicular to the surface. We measured their infrared (IR) reflectivity spectra and assignments of the phonon oscillators were made. The optical conductivity of Tl2122 and Tl2223 phases in the normal state have been obtained from measurements of the reflectivity over a wide frequency range. The position of the plasma peak is tentatively determined.     

Relaxation of the magnetic structures in high temperature superconducting ceramics Tl2Ca2Ba2Cu3Ox. Investigation of the microwave response

A new method to study relaxation of magnetic structures is suggested, based on the observation of the relaxation of microwave response. A new explanation of these processes is proposed, using the theory of “polychromatic” kinetics in the solid state.     

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     

Growth of Bi2Sr2Cu1Ox films by laser ablation

The formation and the properties of thin BiSrCuO films grown on MgO single crystal substrates by the pulsed laser ablation of a Bi₂Sr₂Cu₁O₆ target have been studied. The precise influence of the oxygen pressure and substrate temperature on the atomic composition, nature and structure of the grown phases, crystalline quality and superconductivity of the films has been analyzed. In the 600–750°C temperature range and 0.05–0.5 mbar oxygen pressure range, highly textured films of the 2201 phase (Bi₂Sr₂Cu₁O₆ phase) were formed despite large composition deviations (Bi enrichment and Sr depletion) with respect to the ideal composition. A high crystalline quality was evidenced for films grown at low and intermediate pressure and high temperature. χ_min values in the films deduced from channeling experiments were similar to the case of single crystal material. Despite this high crystalline quality, incomplete or very low T_c superconducting transitions were observed in the resistivity measurements.     

FAR-INFRARED AND INFRARED REFLECTIONS OF Tl2Ba2Ca2Cu3O10 FILM

The far-infrared and infrared reflection spectra of Tl₂Ba₂Ca₂Cu₃O₁₀ superconducting film are reported in this paper. It is found there are three sharp reflection edges in both the superconducting and normal states, their positions being near ≈ 150, ≈ 350 and ≈600 cm^-1. We attribute these reflection spectra to the Drude free carriers and a wide mid-infrared absorption band. When the incident angle increases from 7° to 30°, some additional stractures appear in the refiection spectra, which are the A_2u phonon modes vibrating along c-axis.