Fluxoid quantization and phase transition in hollow superconductors carring transport current

1973 ◽  
Vol 6 (9) ◽  
pp. 329-335 ◽  
Author(s):  
M. Rabinowitz ◽  
E. L. Garwin
Keyword(s):  
Phase Transition ◽  
Transport Current ◽  
Fluxoid Quantization

scholarly journals A short-time physics problem in superconductivity: Stability against quench

2020 ◽  
Vol 49 (1-2) ◽  
pp. 173-195 ◽  
Author(s):  
HARALD REISS
Keyword(s):  
Phase Transition ◽  
Cross Section ◽  
Transport Current ◽  
Transient Temperature ◽  
Conducting Phase ◽  
Flux Flow ◽  
Flow Losses ◽  
Numerical Finite Element ◽  
The Stability ◽  
Short Time

This paper investigates the stability problem of superconductors against quench. Numerical Finite Element simulations are applied to calculate the distribution of transient temperature, critical current density and transport current in the conductor cross-section under a disturbance, here flux flow losses. Contrary to standard stability models, the focus of the paper is on situations very close to the superconducting/normal conducting phase transition. The obtained results demonstrate it is not realistic, even in thin films, to assume uniform conductor temperature under a disturbance. A method is suggested on how to predict the time and position of a quench when it is expected to occur in the conductor cross-section. Quench starts locally. Application of a microscopic stability model allows to describe continuous, not abrupt but very fast break-down of transport current in situations close to the phase transition.

THE TEMPERATURE DEPENDENCE OF RESISTANCE AND CRITICAL CURRENT IN GRANULAR YBa2Cu3Ox SUPERCONDUCTING FILMS

1989 ◽  
Vol 03 (09) ◽  
pp. 729-734 ◽  
Author(s):  
V. ŠTRBÍK ◽  
Š. BEŇAČKA ◽  
Š. GAŽI ◽  
Š. CHROMIK ◽  
J. LEVÁRSKY ◽  
...  
Keyword(s):  
Thin Films ◽  
Phase Transition ◽  
Temperature Dependence ◽  
Critical Current ◽  
Superconducting Films ◽  
Transport Current ◽  
Superconducting Phase ◽  
Normal Metal ◽  
Superconducting Phase Transition

Temperature dependence of resistance R(T) and critical transport current I c (T) was measured for high-Tc YBa 2 Cu 3 O x granular thin films prepared by vacuum co-evaporation. The results are interpreted in terms of superconductor-constriction-superconductor (ScS) or superconductor-normal metal-superconductor (SNS) models, shown to be more adequate than the superconductor-insulator-superconductor (SIS) one. The films with nearly the same superconducting phase transition can exhibit both metallic (dR/dT>0) or semiconductor (dR/dT<0) behavior at T>Tcon. This is ascribed to intragranular defects which are shunted below T con .

Microstructure of laser-irradiated, conducting Kapton polyimide

1995 ◽  
Vol 53 ◽  
pp. 502-503
Author(s):  
D. L. Callahan ◽  
Z. Ball ◽  
H. M. Phillips ◽  
R. Sauerbrey
Keyword(s):  
Electron Microscopy ◽  
Phase Transition ◽  
Transmission Electron Microscopy ◽  
Cross Section ◽  
Film Surface ◽  
Cross Sectional ◽  
General Utility ◽  
Transmission Electron ◽  
Considerable Debate ◽  
Potential Applications

Ultraviolet laser-irradiation can be used to induce an insulator-to-conductor phase transition on the surface of Kapton polyimide. Such structures have potential applications as resistors or conductors for VLSI applications as well as general utility electrodes. Although the percolative nature of the phase transformation has been well-established, there has been little definitive work on the mechanism or extent of transformation. In particular, there has been considerable debate about whether or not the transition is primarily photothermal in nature, as we propose, or photochemical. In this study, cross-sectional optical microscopy and transmission electron microscopy are utilized to characterize the nature of microstructural changes associated with the laser-induced pyrolysis of polyimide.Laser-modified polyimide samples initially 12 μm thick were prepared in cross-section by standard ultramicrotomy. Resulting contraction in parallel to the film surface has led to distortions in apparent magnification. The scale bars shown are calibrated for the direction normal to the film surface only.

The structure of membranes and membrane proteins embedded in amorphous ice

1992 ◽  
Vol 50 (1) ◽  
pp. 432-433
Author(s):  
Uwe Lücken ◽  
Joachim Jäger
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Membrane Proteins ◽  
Phase Transition Temperature ◽  
Lipid Vesicles ◽  
Freezing Stress ◽  
Amorphous Ice ◽  
Different Temperatures ◽  
Band Pass ◽  
Lipid Polymorphism

TEM imaging of frozen-hydrated lipid vesicles has been done by several groups Thermotrophic and lyotrophic polymorphism has been reported. By using image processing, computer simulation and tilt experiments, we tried to learn about the influence of freezing-stress and defocus artifacts on the lipid polymorphism and fine structure of the bilayer profile. We show integrated membrane proteins do modulate the bilayer structure and the morphology of the vesicles.Phase transitions of DMPC vesicles were visualized after freezing under equilibrium conditions at different temperatures in a controlled-environment vitrification system. Below the main phase transition temperature of 24°C (Fig. 1), vesicles show a facetted appearance due to the quasicrystalline areas. A gradual increase in temperature leads to melting processes with different morphology in the bilayer profile. Far above the phase transition temperature the bilayer profile is still present. In the band-pass-filtered images (Fig. 2) no significant change in the width of the bilayer profile is visible.

Study of segregation in La1.8Sr0.2CuO4 superconductor by STEM-EDS microanalysis

1987 ◽  
Vol 45 ◽  
pp. 54-55
Author(s):  
T. F. Kelly ◽  
P. J. Lee ◽  
E. E. Hellstrom ◽  
D. C. Larbalestier
Keyword(s):  
Rare Earth ◽  
High Field ◽  
Transport Current ◽  
Total Thickness ◽  
New Class ◽  
Ceramic Superconductors ◽  
Current Densities ◽  
Group Ii ◽  
Eds Microanalysis

Recently there has been much excitement over a new class of high Tc (>30 K) ceramic superconductors of the form A1-xBxCuO4-x, where A is a rare earth and B is from Group II. Unfortunately these materials have only been able to support small transport current densities 1-10 A/cm2. It is very desirable to increase these values by 2 to 3 orders of magnitude for useful high field applications. The reason for these small transport currents is as yet unknown. Evidence has, however, been presented for superconducting clusters on a 50-100 nm scale and on a 1-3 μm scale. We therefore planned a detailed TEM and STEM microanalysis study in order to see whether any evidence for the clusters could be seen.A La1.8Sr0.2Cu04 pellet was cut into 1 mm thick slices from which 3 mm discs were cut. The discs were subsequently mechanically ground to 100 μm total thickness and dimpled to 20 μm thickness at the center.

Electron Microscope study of commensurate-incommensurate phase transition in BaZnGeO4

1990 ◽  
Vol 48 (4) ◽  
pp. 172-173
Author(s):  
Naoki Yamamoto ◽  
Makoto Kikuchi ◽  
Tooru Atake ◽  
Akihiro Hamano ◽  
Yasutoshi Saito
Keyword(s):  
Phase Transition ◽  
Electron Microscope Study ◽  
Room Temperature ◽  
Hexagonal Lattice ◽  
Ferroelectric Materials ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Periodic Arrays ◽  
Modulation Wave Vector

BaZnGeO4 undergoes many phase transitions from I to V phase. The highest temperature phase I has a BaAl2O4 type structure with a hexagonal lattice. Recent X-ray diffraction study showed that the incommensurate (IC) lattice modulation appears along the c axis in the III and IV phases with a period of about 4c, and a commensurate (C) phase with a modulated period of 4c exists between the III and IV phases in the narrow temperature region (—58°C to —47°C on cooling), called the III' phase. The modulations in the IC phases are considered displacive type, but the detailed structures have not been studied. It is also not clear whether the modulation changes into periodic arrays of discommensurations (DC’s) near the III-III' and IV-V phase transition temperature as found in the ferroelectric materials such as Rb2ZnCl4.At room temperature (III phase) satellite reflections were seen around the fundamental reflections in a diffraction pattern (Fig.1) and they aligned along a certain direction deviated from the c* direction, which indicates that the modulation wave vector q tilts from the c* axis. The tilt angle is about 2 degree at room temperature and depends on temperature.

Dynamic low-dose electron diffraction and imaging of phase transitions in polymers

1993 ◽  
Vol 51 ◽  
pp. 890-891
Author(s):  
David C. Martin ◽  
Jun Liao
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Electron Diffraction ◽  
Low Dose ◽  
Dark Field ◽  
Continuous Change ◽  
Selected Area Electron Diffraction ◽  
Resolution Electron ◽  
Chain Axis ◽  
High Resolution Electron Micrographs

By careful control of the electron beam it is possible to simultaneously induce and observe the phase transformation from monomer to polymer in certain solid-state polymcrizable diacetylenes. The continuous change in the crystal structure from DCHD diacetylene monomer (a=1.76 nm, b=1.36 nm, c=0.455 nm, γ=94 degrees, P2l/c) to polymer (a=1.74 nm, b=1.29 nm, c=0.49 nm, γ=108 degrees, P2l/c) occurs at a characteristic dose (10−4C/cm2) which is five orders of magnitude smaller than the critical end point dose (20 C/cm2). Previously we discussed the progress of this phase transition primarily as observed down the [001] zone (the chain axis direction). Here we report on the associated changes of the dark field (DF) images and selected area electron diffraction (SAED) patterns of the crystals as observed from the side (i.e., in the [hk0] zones).High resolution electron micrographs (HREM), DF images, and SAED patterns were obtained on a JEOL 4000 EX HREM operating at 400 kV.

Single Crystal Raman Spectra of the Phase Transition in KTCNQ

1982 ◽  
Vol 85 (1) ◽  
pp. 297-303 ◽  
Author(s):  
A. D. Bandrauk ◽  
K. D. Truong ◽  
S. Jandl
Keyword(s):  
Phase Transition ◽  
Single Crystal ◽  
Raman Spectra
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