THE COMPOSITION AND STRUCTURE OF Y-Ba-Cu-O SUPERCONDUCTORS

1987 ◽  
Vol 01 (02) ◽  
pp. 341-349
Author(s):  
Z.Y. Hua ◽  
C.L. Jia ◽  
H.S. Cheng ◽  
Y.M. Cai ◽  
A.R. Jiang
Keyword(s):  
Single Phase ◽  
Nominal Composition ◽  
High Tc Superconductors ◽  
Small Particles ◽  
High Tc ◽  
Third Phase ◽  
Composition And Structure ◽  
The Difference ◽  
Phase Phase ◽  
Superconductive Phase

High Tc superconductors of Y-Ba-Cu-O system with (Y+Ba):Cu=1~2 have been investigated. Results show that any sample in this system with a proportion of Y:Cu between 0.6 and 1.2 is oxygen-deficient and will be superconductive after sintering in an oxygen flow. In this system all superconductors with different nominal composition have a superconductive phase of perovskite-1ike YBa2Cu3O7 (Phase A), and the difference of constituents is shown in another phase (Phase B) which acts as a gettering center. When the composition has an excess of Y, there will be a third phase (Phase C) which has been identified as small particles of Y2O3 . For an exact nominal proportion of Y:Ba:Cu=1:2:3 , single-phase superconductors can be prepared.

LOW TEMPERATURE ELASTIC BEHAVIOR OF POTASSIUM-DOPED Bi-2212 SINGLE PHASE HIGH Tc SUPERCONDUCTORS

1994 ◽  
Vol 08 (18) ◽  
pp. 1097-1106 ◽  
Author(s):  
B. GOPALA KRISHNA ◽  
R. RAVINDER REDDY ◽  
P. VENUGOPAL REDDY ◽  
S. V. SURYANARAYANA
Keyword(s):  
Single Phase ◽  
Longitudinal Velocity ◽  
Solid State Reaction Method ◽  
Elastic Behavior ◽  
Velocity Measurements ◽  
High Tc Superconductors ◽  
Qualitative Explanation ◽  
High Tc ◽  
Pulse Transmission ◽  
Transmission Technique

A single phase Bi-2212 and two potassium-doped Bi-2212 samples have been prepared by the solid state reaction method. After the usual characterisation, the ultrasonic longitudinal velocity measurements of all the samples over a temperature range of 80–300 K were undertaken by the pulse transmission technique. The longitudinal velocity of the undoped sample is found to vary in an anomalous way followed by a maximum at 140 K. On the other hand, in the case of the two K-doped ones, the velocity is found to vary with temperature in a normal way up to 120 K followed by a maximum at 105 and 100 K respectively. A qualitative explanation for the observed behavior in all the three cases is given.

Microstructure of a Y2Ba2Cu3O7-Σ superconductor pellet prepared by shock consolidation

1988 ◽  
Vol 46 ◽  
pp. 952-953
Author(s):  
R. F. Antrim ◽  
J. Marti ◽  
Z. Iqbal
Keyword(s):  
Shock Wave ◽  
High Temperature ◽  
Thin Film Deposition ◽  
Film Deposition ◽  
Nominal Composition ◽  
High Tc Superconductors ◽  
High Tc ◽  
Shock Compaction ◽  
High Pressure High Temperature

R&D in high Tc superconductors encompasses two broad areas, namely, 1) synthesis and characterization of high Tc superconducting powders and 2) consolidation of the powders into useful parts. In the latter area, techniques such as thin film deposition, high temperature sintering of the powders and continuous casting are being pursued by various groups. Another technique which could prove useful in the fabrication of larger pieces is that of shock compaction. In this approach, explosives are used to propel a piston, resulting in a shock wave which leads to high pressure- high temperature consolidation of the powder. In this report we examine the microstructure that results when a superconducting powder was consolidated into a pellet using the shock-loading technique.The nominal composition of the starting powder was Y1Ba2Cu3O7δ (“123”). Explosives were used to create a shock-wave with an estimated peak pressure of 60 GPa and temperatures of about 800°C.

AC susceptibility of the sintered Bi1.6Pb0.4Sr2(Ca1-xMx)2Cu3Oδbulk high-Tc superconductors

2001 ◽  
Vol 689 ◽  
Author(s):  
Malik I Adam ◽  
Abdul Halim Shaari ◽  
Zainul A Hassan ◽  
Kaida Khalid
Keyword(s):  
Ac Susceptibility ◽  
Field Amplitude ◽  
Nominal Composition ◽  
Temperature Peak ◽  
High Tc Superconductors ◽  
Reaction Route ◽  
Pinning Mechanism ◽  
High Tc ◽  
Ac Field ◽  
Qualitative Discussion

ABSTRACTAC susceptibility measurements as a function of temperature, frequency and applied ac field amplitude were performed on two rectangular bar shaped samples of nominal composition Bi1.6Pb0.4Sr2(Ca1-xMx)2Cu3Oδ, with M=Pr, Gd, and x=0.01, obtained by the usual solid state reaction route. The incorporation of the rare earth elements at low concentration stage results in an improvement of grain connectivity for the sample doped with Pr. On the other end, the ac field amplitude and frequency dependence of the susceptibility curves disclosed bulk pinning hystersis loss feature. The potential barrier height, activation energy at the grain boundary extracted from the low temperature peak revealed that flux creep is governing the pinning mechanism inside the samples. Qualitative discussion in the framework of the critical state model was highlighted

The Single Phase Regions and the Phase Stability of the High-Tc Superconducting Compounds Bi2+x(Sr,Ca)3Cu2O8+d (2212) and Bi2−x(Sr,Ca)4Cu3O10+d (2223)

1992 ◽  
Vol 275 ◽  
Author(s):  
Peter Majewski ◽  
Bernhard Hettich
Keyword(s):  
Chemical Composition ◽  
Phase Stability ◽  
Single Phase ◽  
Phase Region ◽  
Nominal Composition ◽  
Volume Percent ◽  
High Tc ◽  
Single Phase Region ◽  
Cu Content ◽  
Superconducting Compounds

ABSTRACTThe 2212 phase exhibits an extended single phase region having a variable Sr/Ca ratio and Bi-content of 2.1 < Bi < 2.3. At T = 820°C the single phase region extends between 2.05/0.95 > Sr/Ca > 1.2/1.8, whereas, at T = 870° C the single phase region extends between 2.2/0.8 > Sr/Ca > 1.6/1.4. The 2223 phase exhibits a significant higher Bi-content of Bi ∼ 2.5 compared to the formal composition Bi2Sr2Ca2Cu3O10. The Sr/Ca ratio varies between 2/2 > Sr/Ca > 1.9/2.1 reffering to Cu-content of Cu = 3. Samples with the nominal composition Bi2.5Sr2Ca2Cu3Ox and Bi2.5Sr1.9Ca2.1Cu3Ox have been sintered at 880 – 885°C for 90 h in air and consist of 90 – 95 volume percent 2223 phase. Tc depends on the chemical composition of the phases. With decreasing Ca- and Bi-content of the phases Tc increases. Both phases are metastable at roomtemperature. 2212 and 2223 rapidly decompose at 600 °C and 800 °C in air, respectively. At 300°c two new Bi-Sr-Cuprates have been found.

APPLICATION OF ESR TO HIGH-Tc SUPERCONDUCTORS AND RELATED MATERIALS II: ESR of Cu2+ AS A PROBE OF CRYSTAL GROWTH RATES OF Y2BaCuO5 IN THE MELTS OF Y1.8Ba2.4Cu3.4Ox

1999 ◽  
Vol 13 (02) ◽  
pp. 43-50
Author(s):  
K. YAMAMOTO ◽  
S. KAWASHIMA ◽  
K. HOTTA ◽  
K. SUGAWARA ◽  
H. HIROSE
Keyword(s):  
Heat Treatment ◽  
Crystal Growth ◽  
Treatment Period ◽  
Growth Rates ◽  
Heat Treatment Temperature ◽  
Treatment Temperature ◽  
Nominal Composition ◽  
High Tc Superconductors ◽  
High Tc

The effects of heat-treatment temperature (HTT) and heat-treatment period (HTP) on the growth rates of Y 2 BaCuO 5 in the melts with nominal composition of Y: Ba : Cu = 1.8 : 2.4 : 3.4 have been investigated. The ranges of HTT and HTP are 1000~1400° C and 1~120 minutes, respectively. The quantities of Cu 2+ in Y 2 BaCuO 5 have been obtained by ESR, and its growth rates in the aforementioned melts have been quantitatively measured as functions of HTT and HTP.

Preparation of Bi based high-Tc superconductors containing Pb and Sb by the sol-gel method

1992 ◽  
Vol 7 (2) ◽  
pp. 292-298 ◽  
Author(s):  
Y. Masuda ◽  
R. Ogawa ◽  
Y. Kawate ◽  
T. Tateishi ◽  
N. Hara
Keyword(s):  
Sol Gel ◽  
Reaction Scheme ◽  
Nominal Composition ◽  
High Tc Superconductors ◽  
High Tc ◽  
Gel Method ◽  
Sol Gel Method

Preparation of Bi based high-Tc superconductors having Pb and Sb elements has been attempted using the sol-gel method. Production of the high-Tc phase was promoted by doping a little Sb (0.05 mol) together with Pb. The nominal composition of the system is Bi0.96Pb0.19Sb0.05Sr1.0Ca1.1Cu1.6Oy. It has been found that the reaction scheme of Sb doped samples is different from that of Sb nondoped samples.

Comparison of the Hole Conductivities in Ceramic Cuprate Semiconductors and High-Tc Superconductors, as Reflected in the Difference between Oxygen and Copper Madelung Site Potentials

1989 ◽  
Vol 156 ◽  
Author(s):  
Robert K. Metzger ◽  
Jerry B. Torrance
Keyword(s):  
Charge Carriers ◽  
Potential Difference ◽  
High Tc Superconductors ◽  
High Tc ◽  
Cuprate Semiconductors ◽  
The Difference

ABSTRACTThe Madelung energies of 18 cuprates and 1 nickelate with sheets or chains of Cu and O have been computed, along with the relevant Madelung site potentials for O and Cu. The difference between these site potentials has been shown to correlate extremely well with the conductivity of these cuprates: only if the site potential difference is intermediate can the holes (the presumed charge carriers) move more easily between Cu and O sites in the CuO2 sheets.

Single phase high Tc superconductors of the bismuth cuprate family

1990 ◽  
Vol 88 (1) ◽  
pp. 183-187 ◽  
Author(s):  
Lina Ben-Dor ◽  
H. Diab ◽  
I. Felner
Keyword(s):  
Single Phase ◽  
High Tc Superconductors ◽  
High Tc

The many faces of STEM in materials science

1991 ◽  
Vol 49 ◽  
pp. 440-441
Author(s):  
John Silcox
Keyword(s):  
Materials Science ◽  
Auger Spectroscopy ◽  
Dark Field ◽  
High Tc Superconductors ◽  
High Tc ◽  
Acoustic Environment ◽  
Electromagnetic Vibration ◽  
The Many ◽  
Serial Mode

Determination of the microstructure and microchemistry of small features often provides the insight needed for the understanding of processes in real materials. In many cases, it is not adequate to use microscopy alone. Microdiffraction and microspectroscopic information such as EELS, X-ray microprobe analysis and Auger spectroscopy can all contribute vital parts of the picture. For a number of reasons, dedicated STEM offers considerable promise as a quantitative instrument. In this paper, we review progress towards effective quantitative use of STEM with illustrations drawn from studies of high Tc superconductors, compound semiconductors and metallization of H-terminated silicon.Intrinsically, STEM is a quantitative instrument. Images are acquired directly by detectors in serial mode which is particularly convenient for digital image acquisition, control and display. The VG HB501A at Cornell has been installed in a particularly stable electromagnetic, vibration and acoustic environment. Care has been paid to achieving UHV conditions (i.e., 10-10 Torr). Finally, it has been interfaced with a VAX 3200 work station by Kirkland. This permits, for example, the acquisition of bright field (or energy loss) images and dark field images simultaneously as quantitative arrays in perfect registration.

TEM investigations of surface residual stress relaxation in A12O3 and Al2O3-SiC nanocomposite

1994 ◽  
Vol 52 ◽  
pp. 628-629
Author(s):  
J. Fang ◽  
H. M. Chan ◽  
M. P. Harmer
Keyword(s):  
Residual Stress ◽  
Single Phase ◽  
Stress Relief ◽  
Stress Recovery ◽  
Surface Residual Stress ◽  
Microscopic Mechanism ◽  
Sic Particles ◽  
Annealing Procedure ◽  
The Difference ◽  
Nano Size

It was Niihara et al. who first discovered that the fracture strength of Al2O3 can be increased by incorporating as little as 5 vol.% of nano-size SiC particles (>1000 MPa), and that the strength would be improved further by a simple annealing procedure (>1500 MPa). This discovery has stimulated intense interest on Al2O3/SiC nanocomposites. Recent indentation studies by Fang et al. have shown that residual stress relief was more difficult in the nanocomposite than in pure Al2O3. In the present work, TEM was employed to investigate the microscopic mechanism(s) for the difference in the residual stress recovery in these two materials.Bulk samples of hot-pressed single phase Al2O3, and Al2O3 containing 5 vol.% 0.15 μm SiC particles were simultaneously polished with 15 μm diamond compound. Each sample was cut into two pieces, one of which was subsequently annealed at 1300° for 2 hours in flowing argon. Disks of 3 mm in diameter were cut from bulk samples.

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