Enhancement of thermopower in the highT c superconductor YBa2Cu3O7 and related compounds
TL;DR: In this article, the absolute thermopower of single phase YBa2Cu3O7 and Y0.8Er0.2Ba2C 3O7 has been measured in the range 250 K to the superconducting transition temperature.
Abstract: The absolute thermopower of single phase YBa2Cu3O7 and Y0.8Er0.2Ba2Cu3O7 has been measured in the range 250 K to the superconducting transition temperature. It is found that these compounds show a large enhancement of thermopower in the range 150 K down toT
c. This enhancement shows a steep exponential drop as the temperature increases from the transition temperature. The temperature variation of the enhancement is too steep to be accounted for by electron-phonon or electron-local structural excitation mechanisms.
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TL;DR: In this article, the thermoelectric power of Y1Ba2Cu3O7−y has been precisely measured in absence of, but also under applied (small) magnetic fields over a large temperature range [65 −230 K].
Abstract: The thermoelectric power (TEP) of Y1Ba2Cu3O7−y has been precisely measured in absence of, but also under applied (small) magnetic fields over a large temperature range [65–230 K]. The thermoelectric power is positive for all field values. The knee observed on the magneto-resistivity below the so-called “critical temperature” is observed here as well. An anomalous hysteresis is found. The temperature derivative of the TEP at Tc is analyzed on a log-log plot. Discussion of the peak above Tc, and of the sometimes observed negative dip below Tc is presented.
38 citations
TL;DR: In this paper, the lower limit of G.L. breakdown temperature appears to be strongly dependent on the silver concentration in YBa2Cu3.05Ox pellets and the critical exponent of critical exponent = −0.28.
Abstract: Temperature dependence of electrical resistivity and thermoelectric power of (YBa2Cu3.05Ox)Agn pellets are reported. Data on electrical conductivity near T >Tc are studied in terms of AL formulations. The lower limit of G.L. breakdown temperature appears to be strongly dependent on silver concentration. Apart from usual 2D and 3D regions, with increase of silver content in YBaCuO a third region close to Tc is revealed having critical exponent = −0.28. Thermoelectric power was found to follow a relation of the type S = AT + BT. Analysis of our data indicates that the TEP precursor peak near T >Tc arises due to superconducting fluctuations.
26 citations
TL;DR: In this article, the authors have performed neutron-diffraction and thermopower experiments on two samples of NdSrBaCu 3 O 6+ z, one was a conventionally annealed sample at 450°C in oxygen [O] and the other was heated in argon at 850°C followed by oxygen annealing [AO].
Abstract: We have performed neutron-diffraction and thermopower experiments on two samples of NdSrBaCu 3 O 6+ z . One was a conventionally annealed sample at 450°C in oxygen [O] and the other was heated in argon at 850°C followed by oxygen annealing [AO]. The T c of the sample [O] was 68 K and that of [AO] was 78 K. The neutron data showed that the [O] sample had a higher impurity level arising from Nd entering the Sr/Ba sites that may result in a decrease in the carrier density ( p ) which was also confirmed by our thermopower measurements. The increase in p and in-phase purity for the [AO] sample may account for the observed increase in T c .
15 citations
TL;DR: In this article, temperature dependence of electrical resistivity and thermoelectric power of undoped Y-Ba-Cu-O sintered pellet and that doped with small amount of sulphur and silver are presented.
Abstract: Temperature dependence of electrical resistivity and thermoelectric power of undoped Y-Ba-Cu-O sintered pellet and that doped with small amount of sulphur and silver are presented. While the nature of the temperature dependence of electrical resistivity and thermoelectric power remains similar, their absolute values are strongly influenced by the presence of the dopant. Thermoelectric power data for all the samples can be fitted to an expression of the type, S = AT +B/T. It is argued from the data that the precursor peak in thermoelectric power near T > Tc is of electronic origin due to superconducting fluctuations.
11 citations
TL;DR: In this paper, the title compounds have been synthesized and studied with a view to stabilize the 123 structure and achieve single phase formation and the results of thermopower on two of the single phase compounds (x=0.1 and 0.2) show a negative thermop power at all temperatures above T C with temperature dependence similar to that of Y-123.
Abstract: The title compounds have been synthesized and studied with a view to stabilize the 123 structure and achieve single phase formation. Single phase and high T C are obtained with Sr content as low as x=0.1 in the case of Yb. The single phase region extends only up to x=0.5, in contrast to the Sr substituted Y-123 system wherein the single phase region has been established up to x=1.2. The T C , zero decreases systematically with increase in x. Preliminary results of thermopower on two of the single phase compounds (x=0.1 and 0.2) show a negative thermopower at all temperatures above T C with temperature dependence similar to that of Y-123. In the case of Lu, Sr substitution does not completely stabilise the 123 phase for any x. However, the quantity of the 123 phase is increased significantly for x=0.4 –0.5 when compared to x=0.0. Structural, electrical and magnetic data are discussed.
11 citations
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TL;DR: A stable and reproducible superconductivity transition between 80 and 93 K has been unambiguously observed both resistively and magnetically in a new Y-Ba-Cu-O compound system at ambient pressure.
Abstract: A stable and reproducible superconductivity transition between 80 and 93 K has been unambiguously observed both resistively and magnetically in a new Y-Ba-Cu-O compound system at ambient pressure. An estimated upper critical field H c2(0) between 80 and 180 T was obtained.
5,965 citations
TL;DR: In this article, the authors reported the isolation of the pure oxide phase responsible for high Tc superconductivity, which has the composition Y0.33Ba 0.33±δ, with an oxygen defect perovskite structure.
Abstract: The discovery of La–Ba(Sr)–Cu oxides of K2NiF4 structure exhibiting superconductivity in the 30–40 K region was reported early this year1. The recent announcement of superconductivity above the temperature of liquid nitrogen in Y–Ba–Cu oxides2 has belied all expectations. Unfortunately, all the Y–Ba–Cu oxide compositions exhibiting this remarkable feature were biphasic or multiphasic. We have studied various compositions of the Y3–xBa3+xCu6O14 and now report the isolation of the pure oxide phase responsible for high Tc superconductivity. This oxide has the composition Y0.33Ba0.67CuO2.33±δ, with an oxygen defect perovskite structure. The pure oxide shows the onset of superconductivity at 120 K, attaining zero resistance at 87 K. It also exhibits the highest Meissner effect of all the high-Tc oxide superconductors.
107 citations
37 citations
TL;DR: The oxide responsible for high-temperature superconductivity (onet ∼100 K, zero resistance above liquid N2 temperature) was found to be YBa2Cu3O7±δ as mentioned in this paper.
Abstract: The oxide responsible for high-temperature superconductivity (onset ∼100 K, zero resistance above liquid N2 temperature) is found to be YBa2Cu3O7±δ.
26 citations