Bi Sr Ca Research Articles

The in-situ preparation of Bi 2Sr 2CaCu 2O 8 + δ films using the pulsed-laser deposition technique

BiSrCaCuO thin films were deposited on (100)-oriented MgO single crystals using the pulsed-laser deposition technique and targets of nominal composition Bi 2Sr 2CaCu 2O 8 + δ ( i.e. ( [ Bi]:[ Sr]:[ Ca]:[ Cu] = )2:2:1:2 ) with the mass density larger than 90% of the theoretical value. To obtain an in-situ process of producing single-phase 2:2:1:2 films, we varied three parameters, namely the substrate temperature, the oxygen pressure and the distance between the target and substrate. The results of surface studies using scanning electron microscopy, energy-dispersive X-ray analysis, the superconducting transition temperature and the critical current density are discussed.

Polymeric precursors for the preparation of Bi 1.5Pb 0.5Sr 2Ca 2Cu 3O x

The Pechini process has been used to prepare bulk Bi(Pb)SrCaCuO superconductors by employing the polymeric citric acid/ethylene glycol (CA/G) derived precursors. With appropriate heat treatment these precursors can be converted into a pure Bi 1.5Pb 0.5Sr 2Ca 2Cu 3O x superconductor with T c in the range of 100–110 K and with good stoichiometry control and uniform grain size. The chemistry involved in the materials processing leading to the formation of the superconductor and the results of X-ray diffraction, infrared spectroscopy, thermal analysis (DTA/TGA), and SEM morphological studies obtained in our investigations on the precursors as well as the oxide superconductors are presented.

Target phase composition effect on BiPbSrCaCuO thin films deposited by laser ablation

The superconducting transition temperature T c of thin films of lead-doped BiSrCaCuO produced by laser ablation has been found to depend on the phase composition of the bulk target. Laser ionization mass analysis studies of the same material have shown the presence of high mass fragments in the ablation plume. In the film deposition system these fragments would have been deposited on the substrate during the ablation of the target, and they could have acted as “seeding” sites for subsequent film growth, producing heterogeneous rather than homogeneous nucleation.

Laser ablation and deposition of superconducting and dielectric thin films

The growth of thin films of lead-doped BiSrCaCuO, PbSrYCaCuO and CeO 2 by laser ablation and deposition is described. Multilayers of (BiPbSrCaCuO)/PbO were deposited on an MgO(100) single crystal at room temperature. After subsequent annealing a T c, onset of 110 K with a T c, zero of 81 K was obtained. PbSrCaYCuO thin films were grown in situ on single crystals of MgO(100). A T c, onset of 7o K and a T c, zero of 24 K were obtained. With the aim of using CeO 2 as a buffer layer in growing superconducting thin films on silicon, CeO 2 was grown in situ on Si(111) and Si(100) single-crystal substrates. The films were found to be highly oriented in the [111] direction.

Improved barrier layer for high-Tc superconductor on silicon

Buffer layer configurations consisting of magnetron sputtered ZrO2, Zr–Si mixed oxide, and SiO2 were investigated for sputter deposition of Bi–Sr–Ca–Cu–O high‐Tc superconducting thin films onto silicon wafers. A problem associated with film flaking during postdeposition annealing was overcome by burying the sample in a powder of Bi–Sr–Ca–Cu–O material. Crack growth and buckling in the buffer layers, associated with differential thermal expansions, were eliminated by raising the deposition temperature for the buffer layers. Unfortunately, the improved buffer layers were not good enough to prevent substrate–film interactions over the long annealing times (e.g., 14 h), and the sufficiently high temperature (e.g., 850 °C) needed for the formation of the 2223 high Tc (110 K) phase.

A-Axis oriented BiSrCaCuO thin films deposited on (1 0 0 ) MgO substrates by metalorganic chemical vapor deposition

a-Axis oriented BiSrCaCuO thin films weere prepared at substrate temperatures of 720−850°C on (100) MgO substrates by MOCVD. The a-axis oriented BiSrCaCuOthin films were found to grow preferentially at lower substrate temperatures and faster deposition rates. The formation of the a-axis oriented domains was found to be preferential at the ratios of Cu/(Sr+Ca) and Bi/(Sr+Ca) lower than the stoichiometric composition of the 2212 and 2223 phases, while the c-axis oriented domains were found to be preferentially formed at the ratios of Cu/(Sr+Ca) and Bi/(Sr+Ca) higher than the stoichiometric composition of the 2212 and 2223 phases. The surface morphology was found to have characteristic triangular layered grains from the SEM observations, and these grains were aligned with a long dimension along the a-or the b-axis of the MgO substrate.

Laser ablation and deposition of high [formula omitted] superconducting BiSrCaCuO films doped with lead, praseodymium and lithium

High T c superconducting BiSrCaCuO thin films doped with lead, praseodymium and lithium were ablated on MgO(100) substrates at room temperature using a neodymium-doped yttrium aluminium garnet laser at 1064 nm. The effect of annealing conditions on the structural and superconducting properties of the films was investigated. The lead-doped films with [Bi]:[Sr]:[Ca]:[Cu] ratio near 2:2:2:3 annealed for 60 h at 850 °C consisted mainly (above 85%) of the 2:2:2:3 phase. These films had a T c0 above 100 K. The films doped with praseodymium or with praseodymium and lead had poorer superconducting properties than the undoped films do. It was observed that both praseodymium and lithium inhibited the formation of the 2:2:2:3 phase. For lithium-doped films with [Bi]:[Sr]:[Ca]:[Cu] ratios near 2:2:1:2 or 2:2:2:3, T c0 values in the range 83–85 K were obtained. This was an enhancement of 3–6 K compared with the values for the undoped 2:2:1:2 phase films prepared under similar conditions. For the best lithium-doped films, critical currents exceeding 10 4 A cm −2 at 77 K were measured.

Accurate measurement of atomic beam flux by pseudo-double-beam atomic absorption spectroscopy for growth of thin-film oxide superconductors

We report the use of pseudo-double-beam atomic absorption spectroscopy to make very accurate (0.1%–1%) measurements of the beam flux from Knudsen effusion cells in a molecular beam epitaxy system. This system has been used to grow Bi–Sr–Ca–Cu–O–based superconducting thin films and heterostructures in an atomic-layer-by-layer fashion. The resulting material displays excellent crystallographic and transport properties. Atomic absorption measurement of beam fluxes may also be of benefit for other materials systems, such as InGaAs/InP.

Phase separation in BiSrCaCuO melts during quenching

Phase separation is found for the first time in quenched samples of amorphous Bi 2Sr 2Ca 1Cu 2O x (often called “2212” composition). Clear evidemce for metastable phase separation is found using X-ray diffraction (XRD), transmission electron microscopy (TEM), and differential thermal analysis (DTA). This has serious implications for possible fabrication of high current density devices from these compositions, especially via glass-ceramic processing routes.

Phase separated glass and resultant superconducting glass ceramics in BiSrCaCuO (2245) composition

The crystallisation of superconducting phases in a glass of nominal composition Bi 2Sr 2Ca 4Cu 5O y has been found to depend on phase separation within the glass. The most interesting result is the attainment of zero resistance even though the volume fraction of superconducting phase, estimated from Xac measurements, is smaller than 0.1%. These results have been discussed on the basis of exsolution of different phases, partial melting and rearrangement of ions at around grain boundaries. Presumably, a narrow superconducting path is formed along the flow line of the partially melted state.

Strength and critical current density of Bi(Pb)SrCaCuO and YBaCuO in silver-sheathed superconducting tapes

The critical current density at 77 K at 0 T and the tensile strength at room temperature of high T c Bi(Pb)SrCaCuO and YBaCuO oxides in silver-sheathed tapes prepared by the powder-in-tube method were investigated. The main results can be summarized as follows. (1) The critical current density and the strength of both oxides increased with decreasing thickness. (2) The strength of the Bi(Pb)SrCaCuO oxide was 120 MPa at most, being comparable to that of the YBaCuO oxide, but far lower than that of Nb 3Sn compound. (3) When the oxides were weak, the higher the strength, the higher was the current density in both YBaCuO and Bi(Pb)SrCaCuO tapes. The textured structure in the Bi(Pb)SrCaCuO tape with thin oxide raised current density effectively, while it raised the strength only slightly.

Preparation and characterization of high Tc Bi(Pb)SrCaCuO thin films

High T c Bi(Pb)SrCaCuO thin films have been made on MgO substrates by single target RF sputtering. The best film showed sharp XRD peaks indexed to (00 n), indicating that the film is C-axis oriented, with onset and zero resistance at 100 K and 80.2 K, respectively. The microwave response of the film with a constriction indicated the presence of Josephson type weak links limiting the critical current density.

Sensitivity to magnetic field for BiSrCaCuO superconductive film

Bi(Pb)SrCaCuO films prepared by rf magnetron sputtering (film A) and Doctor Blade Casting (film B) were annealed. The films made use of a magnetic detector, based on the magnetoresistive effect in the oxide superconductor. Film sensitivity to a magnetic field was measured. The 842°C annealed film A showed an excellent property as a magnetic detector, and its magnetic field resolution estimated from the sensitivity to the magnetic field and the voltage noise was 1·82 × 10 −6G/ √Hz at 100 Hz. This film was mainly composed of plate-like crystals which were partially parallel and partially perpendicularly oriented to the surface of the MgO substrate. It is considered that the grain boundaries between the grains with different crystal axes act as weak links in this compound. However, film B showed high sensitivity to magnetic field, but the output voltage was noisy and the magnetic field resolution was 4·06 × 10 −4 G/√Hz at 100 Hz.

BiSrCaCuO superconducting films prepared by in-situ melting

Superconducting films of BiSrCaCu oxides have been prepared by directly melting powders of the oxides on MgO and Al 2O 3 substrates and the preparation of BiSrCaCuO superconducting films has been extended to the (Bi, Pb)SrCaCuO system with improved characteristics. Zero-resistivity temperatures, T c0 of up to 95 K have been obtained. The films are highly oriented, with the c axis perpendicular to the substrates. A film with a T c0 of 95 K has been identified to be exclusively of the n = 2 structure, which is consistent, which is consistent with earlier findings of the authors that the n = 2 phase with excess Cu content also contributes the “ high-T c0 ” in this system. Based on the results, this technique, although simple, seems to offer the promise of producing good superconducting films.

Thermal Expansion and Superconductivity in Alkali Metal‐ and Silver‐doped BiSrCaCuO System

AbstractSamples with the nominal composition Bi2Sr2CaCu2Oy with na doped at the Ca site and K doped at the Sr site are prepared by solid state reaction method. From the X‐ray diffraction data it is found that all the the samples have exhibited a single phase 2212. The D.C. electrical resistivity data show that for Na‐doped samples the Tc (zero) varies from 80 K to 85 K and for K‐doped samples it is from 79 K to 82 K. The loss of oxygen from these samples around 400°C was confirmed by high temperature dilatometry. The variation of the thermal expansion coefficient (“α”) with temperature for different alkali dopings are discussed. Also the samples with the nominal composition Bi4Sr3Ca3Cu4−xAgxOy (with x = 0, 0.1, 0.2, 0.3) were studied.

Electrochemical intercalation of alkali metals into superconducting oxide phases

The electrochemical intercalation of alkali metals into several superconducting oxide phases has been carried out by galvanostatic discharge of an electrochemical cell. In each case intercalation appears to result in a decrease in the volume fraction of the superconducting phase. Intercalation of lithium into an indium-doped Bi–Sr–Ca–Cu oxide gave a material of approximate composition Li0.23Bi1.9In0.1Sr2CaCu2O8 +δ, in which the superconducting onset temperature, Tc, was increased by ca. 15 K above that of the original compound. Intercalation into other superconducting bismuth oxides produced increases in Tc in some cases, and decreases in others. Intercalation into the thallium 2212 superconductor produced no discernible change in Tc.

On the search for a stable BiPbSrCaCuO 2223 polytype

A new crystallographic form of the 2223 polymorph has been identified by means of convergent beam electron diffraction, with a c-axis of 36.8 Å and with the space group F2dd. In contrast to the well-known 2223 polymorph of the compound PbBiSrCaCuO with the c-axis of 37.1 Å and a space group of A2aa/Amaa, which has a limited shelf life, the new form is stable at room temperature and in normal atmospheric conditions, but with a slightly lower T c of 102.2 K, with an onset temperature of 103.3 K.

Observation of the initial growth of semiconductor films on the Bi-based superconducting single crystal by RHEED method low temperature reaction of Ge with BSCCO single crystal

We investigated the initial growth of Ge semiconductor films on the clean surface of 80 K phase Bi Sr Ca Cu O(BSCCO) single crystal, using reflection high-energy electron diffraction (RHEED) and X-ray photoelectron spectroscopy (XPS). The growth of Ge was compared with that of Au. The RHEED observation showed that, when Au was deposited up to 100Åon the BSCCO surface at the substrate temperature ( T s) = room temperature (RT= ∼ 20°C) and 300°C, Au grew in an amorphous form and in polycrystalline form, respectively, 20Åthick Ge films deposited on the BSCCO below 300°C were amorphous. The XPS results indicated that Au hardly reacted with the BSCCO, but Ge reacted with the BSCCO at the interface at RT. The formation of the amorphous phase at Ge deposition came from the interface reaction with the BSCCO.

Bi_Sr_Ca_Cu_O superconducting films prepared by in-situ melting

Superconducting films of BiSrCaCu oxides have been prepared by directly melting powders of the oxides on MgO and Al 2 O 3 substrates and the preparation of BiSrCaCuO superconducting films has been extended to the (Bi, Pb)SrCaCuO system with improved characteristics. Zero-resistivity temperatures, T c0 of up to 95 K have been obtained. The films are highly oriented, with the c axis perpendicular to the substrates. A film with a T c0 of 95 K has been identified to be exclusively of the n = 2 structure, which is consistent, which is consistent with earlier findings of the authors that the n = 2 phase with excess Cu content also contributes the “ high -T c 0 ” in this system. Based on the results, this technique, although simple, seems to offer the promise of producing good superconducting films.

Critical currents in silver-sheathed (Bi,Pb)2Sr2Ca2Cu3O10−y superconducting tapes

Nearly 95 vol % of the 110 K superconducting phase was formed by lead doping in a Bi–Sr–Ca–Cu–O system. The processed 110 K superconducting powders were used to produce long silver-sheathed tapes with a highly textured microstructure by rolling and prolonged sintering. The transport critical current density was measured at 4.0 K to be 0.7×105 A/cm2 (the corresponding critical current is 74 A) at zero field and 1.6×104 A/cm2 at 12 T for H∥ab. At 76 K, the critical current density reached a value of ∼1×104 A/cm2 at zero field for H∥ab and gradually decreased to 419 A/cm2 at 1 T. Excellent grain alignment in the a–b plane led to greatly improved critical current densities under a magnetic field. The relationship between the transport properties and the microstructure of the tapes is discussed.