Thallium-based High-temperature Superconductor Research Articles

The effect of O2 pressure on phase formation and superconductivity properties of Tl-based HTS

Thallium-based high-temperature superconductors exhibit excellent superconductivity performance (Tc, Jc). Formation of the Tl-based superconducting materials critically depends on the used precursor and synthesis conditions. In the present investigation, we used the in situ polymerization method for synthesizing high-purity and reaction-ability precursors. We find the critical dependence of Tl-based superconductor phase formation on the quantity of applied oxygen pressure. The experimental results showed that the Tl-1223 phase formed at an oxygen gas pressure at 1 to 2 atm, Tl-2223 phase at 3 atm, and Tl-2212 phase at 4 to 8 atm.

Significance of Cobalt Ferrite Nanoparticles on Superconducting Properties of Tl-1212 High Temperature Superconductor

Thallium-based high temperature superconductor (HTS) with nominal starting composition (Tl0.85Cr0.15)Sr2CaCu2O7-δ (Tl-1212) was prepared using high purity oxide powders via solid state reaction method. Small amounts (0.0 – 0.15 wt. %) of cobalt ferrite nanoparticles (CoFe2O4) were added into Tl-1212 superconductors. The effect of CoFe2O4 nanoparticles addition on the critical temperature (Tc), phase formation and microstructure properties including elemental compositional analysis were studied. The samples were investigated by the characterization of electrical resistance measurement, powder X-ray diffraction method (XRD), scanning electron microscopy and energy dispersive X-ray analysis (EDX). Zero-resistance temperature (Tc-zero) was found to reduce from 97 K to 89 K with increasing of CoFe2O4 nanoparticles concentration. Most of the samples indicated a dominant Tl-1212 phase of a tetragonal structure with a minor phase of Tl-1201. SEM micrographs with EDX mapping showed that CoFe2O4 nanoparticles were well distributed in all the samples.

Effect of graphene addition on the transport critical current density of bulk (Tl0.85Cr0.15) Sr2CaCu2O7-δ superconductor

In this work, the effect of graphene addition on the transport critical current density of (Tl0.85Cr0.15) Sr2CaCu2O7-δ (Tl-1212) superconductor was investigated. Thallium-based high temperature superconductor (HTS) with nominal starting composition (Tl0.85Cr0.15) Sr2CaCu2O7-δ was prepared using high purity oxide powders via solid state reaction method. 0.001 – 0.005 wt.% of graphene were added into Tl-1212 superconductors. The characteristic of the samples were determined by powder X-ray diffraction method, scanning electron microscopy (SEM), energy dispersive X-Ray analysis (EDX), electrical resistance measurements and transport critical current density measurements. The zero-resistance temperature, Tc-zero was found to decrease from 95 K to 84 K with the increase of graphene. The temperature dependence transport critical current density (Jc) of the pure and graphene added bulk samples were investigated. Jc of the non-added bulk sample was 1320 mA/cm2 at 30 K while the Jc of sample with 0.001 wt.% graphene was 3660 mA/cm2 at 30 K. Results showed that the Jc of the Tl-1212 samples decreased with increasing graphene addition. Graphene acted as impurity which is believed to perform the flux pinning effect to Tl-1212. Thus, the Jc of Tl-1212 superconductors was enhanced. The phase formation and morphology of samples Tl-1212 were also discussed in this paper.

Phase Formation and Electrical Transport Properties of Nano-Sized SnO<sub>2</sub> Added (Tl<sub>0.85</sub>Cr<sub>0.15</sub>)Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>7-δ </sub>Superconductors

In this work, the effect of nano-sized SnO2 addition on the phase formation and electrical transport properties of (Tl0.85Cr0.15)Sr2CaCu2O7-δ (Tl-1212) superconductor was investigated. Thallium-based high temperature superconductor (HTS) with nominal starting composition (Tl0.85Cr0.15) Sr2CaCu2O7-δ was prepared using high purity oxide powders via solid state reaction method. Nano-sized SnO2 with 0.01 – 0.05 wt.% were added into Tl-1212 superconductors. The characteristic of the samples were determined by powder X-ray diffraction method (XRD), scanning electron microscopy (SEM), energy dispersive X-Ray analysis (EDX), electrical resistance measurements and transport critical current density measurements. Nano-sized SnO2 added (Tl0.85Cr0.15)Sr2CaCu2O7-δ showed Tc-zero between 93 and 95 K. All of the samples indicated a dominant phase of Tl-1212 with a minor phase of Tl-1201. The highest Jc (at 77 K) was shown by sample with 0.03 wt.% at 3260 mA/cm2. SnO2 has significantly enhanced the transport critical current density of Tl-1212 superconductor by acting as flux pinning centers. However, further addition of nano-sized SnO2 in Tl-1212 superconductor caused degradation in Jc. The SEM micrographs with energy dispersive X-Ray analysis (EDX) showed that SnO2 were well distributed in all the samples.

Thallium-based high-temperature superconductors for beam impedance mitigation in the Future Circular Collider

CERN has recently started a design study for a possible next-generation high-energy hadron–hadron collider (Future Circular Collider—FCC-hh). The FCC-hh study calls for an unprecedented center-of-mass collision energy of 100 TeV, achievable by colliding counter-rotating proton beams with an energy of 50 TeV steered in a 100 km circumference tunnel by superconducting magnets which produce a dipole field of 16 T. The beams emit synchrotron radiation at high power levels, which, to optimize cryogenic efficiency, is absorbed by a beam-facing screen, coated with copper, and held at 50 K in the current design. The surface impedance of this screen has a strong impact on beam stability, and copper at 50 K allows for a limited beam stability margin only. This motivates the exploration of whether high-temperature superconductors (HTS), the only known materials possibly having a surface impedance lower than copper under the required operating conditions, would represent a viable alternative. This paper summarizes the FCC-hh requirements and focuses on identifying the best possible HTS material for this purpose. It reviews in particular the properties of Tl-based HTS, and discusses the consequent motivation for developing a deposition process for such compounds, which should be scalable to the size of the FCC components.

Comment on “Phonons and specific heat in high-T c Tl 1(2)Ba 2Ca n−1 Cu nO 2 n+3(4) superconductors”

Agrawal et al. report results for phonons and phonons specific heat of the thallium-based high-temperature superconductors, obtained from lattice dynamical calculations, based on a model involving only-short-range interactions (Born model). The authors claim that their results are in overall better agreement with experiment than those obtained with the shell model. It is argued here that the Born model neglects important physical characteristics of the high-temperature superconducting compounds and that if phonon dispersion and specific heat data are taken into account, the claim of “better agreement” is unjustified.

Phonon spectra and lattice specific heats of the thallium-based high-temperature superconductors.

We present the phonon-dispersion curves, the one-phonon densities of state, the lattice specific heat {ital c}{sub {ital v}}({ital T}), and the Debye temperatures {ital FTHETA}({ital T}) of the thallium-based high-temperature superconductors, based on full lattice dynamical calculations. Repelling effects due to hybridization of the low-lying transverse acoustic and optical modes lead to small Debye regions of the specific heat ({le}4 K), while the occurrence of low-lying dispersionless transverse modes in the outer parts of the Brillouin zone causes large drops in the Debye temperatures {ital FTHETA}({ital T}) in the range 0 to 20 K. These effects are extremely pronounced in Tl{sub 2}Ca{sub 2}Ba{sub 2}Cu{sub 3}O{sub 10} because of the appearance of very-low-frequency modes.

Superconductor Race Shifts to a New Arena

The search for high-temperature superconductors (HTS) with increasing critical temperatures, {Tc}, seems to have come to a halt. Therefore, promising research in the use of HTS seems to be the new route of approach. Most research is focusing on YBa{sub 2}Cu{sub 3}O{sub x} in various forms. Small specimens of this material have been glued together to produce a single magnet. The ceramic has been fired at a lower temperature to produce smaller grains that do not contain the microcracks found in larger grains, and silver has been added to form a microcomposite both of which improve the mechanical properties of the HTS. Laser ablation has been used to form transite-like devices out of HTS material. A device based on a thallium-based HTS material has been developed at Sandia National Laboratory. This device uses magnetic flux to modulate a current.

Break junction measurement of the tunneling gap of a thallium-based high-temperature superconductor crystal

We have used the break junction method to measure the tunneling gap of a thallium-based high-temperature superconductor crystal in liquid helium at 4 K. The crystal was predominantly Tl2CaBa2Cu2O7 and had a superconducting onset temperature of 105 K. Tunneling data showed a symmetric gap about zero bias between two well-defined conductance peaks in the conductance versus voltage curve. The gap is consistent with a Bardeen–Cooper–Schrieffer energy gap (Δ) of 30 meV assuming a superconductor-insulator-superconductor electrode configuration. In addition, a supercurrent could be detected when the break junction was operated in a point-contact mode at temperatures as high as 95 K.

Ultrasonic attenuation measurements on thallium-based high-temperature superconductors.

We report ultrasonic attenuation measurements on thallium-based high-temperature superconductors with a transition temperature near 110 K. Measurements were carried out between 300 K and liquid-nitrogen temperature. Several peaks were observed with one peak appearing near ${T}_{c}$. At the critical temperature, no sharp drop was noted within our experimental resolution. The attenuation increases with decreasing temperature below ${T}_{c}$. Similar behavior of attenuation measured in Y-based compounds was also observed.

Reproducible, Large-Scale Production of Thallium-Based High-Temperature Superconductors

AbstractThe Rocketdyne Division of Rockwell International has developed a large scale spray-calcination technique generic to the preparation of ceramic high-temperature superconductor (HTSC) powders. Among the advantages of the technique is that of producing uniformly mixed metal oxides on a fine scale. Production of both yttrium and thallium-based HTSCs has been demonstrated using this technique.In the spray calciner, solutions of the desired composition are atomized as a fine mist into a hot gas. Evaporation and calcination are instantaneous, yielding an extremely fine, uniform oxide powder. The calciner is 76 cm in diameter and can produce metal oxide powder at relatively large rates (approximately 100 g/h) without contamination.Bulk samples of thallium-based powder were prepared by spray calcination, collected, cold-pressed, and sintered. An optimized temperature schedule was developed to produce T12Ba2Ca2Cu3Ox. Samples were examined by X-ray diffraction and characterized by measurements of critical transition temperature, Tc. A complete transition to zero resistance at 112 K was measured.

Field and Temperature Dependent Suspension Studies of High Temperature Superconductors

AbstractWe have employed a novel variable-temperature, variable-field/field-gradient cryogenic levitometer, previously used in levitation experiments, to study the suspension properties of the thallium-based high temperature superconductors. Our results are compared and contrasted with the levitation studies and the singular features of the suspension properties are noted.