Thermal expansion of high-T c superconductors

White, G. K.; Driver, R.; Roberts, R. B.

doi:10.1007/bf00534224

Cited by 16 publications

(4 citation statements)

References 13 publications

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“…where j x (t) is the electric current density at depth x from the top surface, j 0 (t) is the electric current density at the top surface, x is the distance from the top surface and d is the depth of electric current penetration. d is given by the expression 19 d~(r=pf m 0 m r ) 1=2…”

Section: Basic Theoriesmentioning

confidence: 99%

“…The current density distribution can be represented as follows 18 where j x ( t ) is the electric current density at depth x from the top surface, j 0 ( t ) is the electric current density at the top surface, x is the distance from the top surface and δ is the depth of electric current penetration. δ is given by the expression 19 where f is the frequency of the electric current, μ 0 is the magnetic susceptibility in a vacuum and μ r = 1 is the relative magnetic susceptibility.…”

Section: Basic Theoriesmentioning

confidence: 99%

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Microstructure evolution in metals induced by high density electric current pulses

Guo

Wang

Dai

2015

Materials Science and Technology

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In this paper, microstructure evolution in metals induced by high density electric current pulses (ECPs) treatment, such as grain refinement, formation of oriented microstructure and redistribution of inclusions, is carefully reviewed. The mechanism for these microstructure evolutions is discussed. It is suggested that there are usually several factors working during ECP: Joule heating (including temperature rise, the heating rate and the cooling rate), stress (including thermal compressive stress, skin effect, electron wind force) and free energy change caused by the current. The Joule heat and the stress usually affect the dynamics, enhance the microstructure evolutions rate, while the free energy change affects the thermodynamics and lowers the barrier of the phase transformation or recrystallisation. The experimental results indicate that high current density ECP provides an effective approach to refine the microstructure of polycrystalline materials and to improve the mechanical properties of the materials.

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Section: Basic Theoriesmentioning

confidence: 99%

Section: Basic Theoriesmentioning

confidence: 99%

Microstructure evolution in metals induced by high density electric current pulses

Guo

Wang

Dai

2015

Materials Science and Technology

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“…The reduction or disappearance of the (020) Bi2212 peak demonstrates that the epitaxy of the Bi2212 films sintered at lower sintering temperature has been improved. At the higher sintering temperature, the epitaxial orientation of Bi2212 films grown on MgO substrates is deteriorated owing to the effect of thermal stress between film and substrate (White et al, 1991). This is because the stress increases with increasing temperature and accelerating cooling rate (the curve of the cooling rate is shown in Fig.…”

Section: Figurementioning

confidence: 99%

Crystalline characteristics and superconducting properties of Bi2212 thin films prepared by the Pechini sol–gel method: the effect of different substrates on the film growth

Miao

Sun

et al. 2015

J Appl Crystallogr

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Bi2Sr2CaCu2O8+δ (Bi2212) superconducting thin films were prepared by the Pechini sol–gel method using nitrates as reactants. The precursor sol was deposited on LaAlO3(100) and MgO(100) single‐crystal substrates via the spin‐coating method. The results revealed that the phase formation temperature region of the pure Bi2212 phase and perfectly epitaxial Bi2212 films deposited on LaAlO3 substrates was significantly expanded to 8 K, indicating an improvement in crystallization of Bi2212 films. In addition, the phase formation temperature region of the pure phase and c‐axis‐grown Bi2212 films deposited on MgO substrates was reduced to 5 K because of the deterioration of epitaxy of Bi2212 films sintered at higher temperature. According to the investigation, the Tc,onset values of Bi2212 films grown on MgO substrates were about 92 K. Meanwhile, the optimal Tc,onset value of Bi2212 superconducting films grown on LaAlO3 substrates rose to 96 K.

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“…Sugano et al [4] measured the thermal expansion of Ag tape by double extensometers between 290 and 5 K. As a result, the thermal expansion curves were confirmed during both the cooling and warming processes to show good agreement with each other for Ag plates with thickness of 3, 1, and 0.2 mm, and the samples' thermal expansion was calculated by a step of 1 K. Using the two-dimensional reciprocal-lattice method of x-ray diffraction, Asahi et al [5] reported the thermal expansion of superconducting Bi-tape in the temperature range between 15 and 300 K. Bagrets et al [6] presented measurements of the thermal conductivity and expansion of the structural materials used for the production of the Rutherford cables in the temperature range from 4 to 300 K. In consideration of polymers, Esposito et al [7] estimated the thermal expansion coefficient of samples using coating of fiber Bragg grating sensors in the temperature range from 4 to 300 K. Numerical models have been proposed to illustrate the tested results. Although some of measurement techniques have been suggested for evaluating the thermal expansion of superconductors [8][9][10], the most measurements on the low-temperature thermal expansion were mainly conducted at randomized temperature variation which can affect the accuracy of sensors. For optimizing superconducting materials and magnets on the viewpoint of engineering design, tensile mechanical properties of superconducting composites at variable cryogenic temperature also come into tremendous notice [11].…”

Section: Introductionmentioning

confidence: 99%

Measurement of Thermal Expansion of Superconducting Wires at Cryogenic Temperature Based on Tensile Method

Xin

Wang

Guan

et al. 2014

J Supercond Nov Magn

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The effects of variable cryogenic temperature on the thermal expansion are measured by tensile method for several commercial superconducting composite wires of NbTi/Cu, Nb 3 Sn/Cu, and high-temperature superconducting (HTS) Bi2212/Ag tapes. A variable temperature cryostat system is constructed to provide successive cooling environment from 300 to 77 K, and a cryogenic-type extensometer is utilized to measure the deformation of the superconducting wires arising from tensile and thermal loadings. In comparison with the mechanical deformation at room temperature, the corresponding thermal deformation at the variable cryogenic temperature is recorded and evaluated during stretching of the superconducting wires. The thermal expansion behavior of the composite wires and superconductor filaments is further captured. It shows that the thermal expansion of NbTi/Cu composite wire, NbTi filaments, Nb 3 Sn/Cu composite wires, and Nb 3 Sn filaments is almost linearly dependent upon the temperature, while those of HTS Bi2212/Ag tapes exhibit notable nonlinear features during cooling of the superconducting wires. In addition, based on the thermal expansion measured from room temperature to liquid nitrogen temperature, the thermal expansions at 4.2 K are extrapolated for lowtemperature composite wires and their filaments, which are compared with the experiments using thermal methods in the existing literature. The results indicate that our variable temperature cryostat system and corresponding tensile method will be an easy way for measuring the thermal parameter of superconducting composite wires.

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Thermal expansion of high-T c superconductors

Cited by 16 publications

References 13 publications

Microstructure evolution in metals induced by high density electric current pulses

Microstructure evolution in metals induced by high density electric current pulses

Crystalline characteristics and superconducting properties of Bi2212 thin films prepared by the Pechini sol–gel method: the effect of different substrates on the film growth

Measurement of Thermal Expansion of Superconducting Wires at Cryogenic Temperature Based on Tensile Method

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