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Journal ArticleDOI

Thermoelectric power in Bi2Sr2−xKxCaCu2Oy

01 Nov 2004-Physica C-superconductivity and Its Applications (North-Holland)-Vol. 415, Iss: 4, pp 209-219
TL;DR: In this paper, the superconducting and normal state transport properties of ceramic samples with composition Bi 2 Sr 2−x K x CaCu 2 O y ( x ǫ = 0, 0.1, 0., 0.2, 0, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12) have been investigated by measuring thermoelectric power.
Abstract: The superconducting and normal state transport properties of ceramic samples with composition Bi 2 Sr 2− x K x CaCu 2 O y ( x = 0, 0.1, 0.2, 0.3, 0.4) have been investigated by measuring thermoelectric power. The samples were prepared by the solid state route, and single phase Bi-2212 was found for all compositions. The T c (0) and thermoelectric power data were collected from 50 to 300 K. The thermoelectric power changes slightly with increasing doping level and increases linearly with decreasing temperature reaching a maximum value at T c (0). The T c (0), hole concentration and thermoelectric data were correlated. The results obtained are analysed in terms of phenomenological theoretical models that makes it possible to determine the band spectrum parameters in the normal state and to trace their changes with varying composition. Following models applied such as (a) Hubbard model, (b) two-band model, (c) Fermi-liquid behaviour. Applicability of these models to the present HTSC system is discussed and the parameters related to the models have been evaluated.
Citations
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Journal ArticleDOI
TL;DR: In this paper, the structural, thermal and transport properties of the glass samples prepared using the glass-ceramic method were investigated, and it was seen that the normal state resistance and hole concentration increases by increasing the Mo level.

26 citations

Journal ArticleDOI
TL;DR: In this paper, the structural, mechanical and transport properties of RuSr2GdCu2O8 sintered between 1000 and 1065 degrees C n O 2 atmosphere have been studied by XRD, microhardness and Seebeck coefficient measurements.
Abstract: The structural, mechanical and transport properties of RuSr2GdCu2O8 sintered between 1000 and 1065 ◦ Ci n O 2 atmosphere have been studied by XRD, microhardness and Seebeck coefficient measurements. The pellets have a tetragonal perovskite-type structure. Microhardness and bulk density of the considered samples increase with increasing sintering temperature. TEP is positive for all samples and decreases with increasing sintering temperature. The normal state TEP data are discussed in view of some theoretical models, namely a two-band model with an additional linear T term and variable range hopping models. (Some figures in this article are in colour only in the electronic version)

18 citations

Journal ArticleDOI
TL;DR: In this paper, the conduction mechanism of gallium antimonide was investigated and the mobility ratio and the effective mass ratio were calculated to be 1.56 and 3.36 respectively.
Abstract: Bulk crystals of gallium antimonide were grown using the vertical Bridgman techniques. The phase formation was confirmed by XRD studies. From dc and ac conductivity measurements, the conduction mechanism was investigated. The mobility ratio and the effective mass ratio were calculated to be 1.56 and 3.36 respectively. The measurements reveal higher values of power factor than the published results for the same compound.

16 citations

Journal ArticleDOI
TL;DR: In this article, the effects of Na substitution for Ca on the activation energies, irreversibility field, upper critical magnetic field and coherence length of polycrystalline Bi2Sr2Ca1−xNaxCu2O8+y have been studied.
Abstract: In the present study, magnetoresistivity performance of polycrystalline Bi2Sr2Ca1−x Na x Cu2O8+y superconductor with x = 0.0, 0.05, 0.075, 0.10, 0.15, and 0.20 has been studied by change of flux pinning mechanism. Samples have been prepared using a polymer solution technique with polyethyleneimine. The effects of Na substitution for Ca on the activation energies, irreversibility field, upper critical magnetic field and coherence length have been studied. The magnetoresistance of samples has been measured at applied magnetic fields between 0 and 9 T. Broadening of superconducting transition has been observed under magnetic field, explained on the basis of Thermally Activated Flux Flow (TAFF) model. The upper critical magnetic field H C2 (0) and the coherence length (ζ(0)) at T = 0 K were calculated using the resistivity data and H C2(0), respectively. H C2 (0) and ξ(0) values have been calculated as 186.4, 195.5, 321.0, 296.0, 292.5, 280.9 T, and 13.29, 12.98, 10.13, 10.55, 10.61, 10.69 A for the 0.0, 0.05, 0.075, 0.10, 0.15, and 0.20 Na-doped samples, respectively. TAFF model has been studied in order to calculate the flux pinning energies. In particular, the flux pinning energies of Bi2Sr2Ca1−xNaxCu2O8+y where x = 0.075 determined to be 0.019 eV for 9 T and 0.239 eV for 0 T.

15 citations

Journal ArticleDOI
TL;DR: In this article, measurements of the electrical resistance (R-T), thermoelectric power (S-T) and thermal conductivity (T) have been carried out on the superconductor Bi1.7Pb0.
Abstract: Measurements of the electrical resistance (R-T), thermoelectric power (S-T) and thermal conductivity (κ-T) have been carried out on the superconductor Bi1.7Pb0.3-x Gd x Sr2Ca3Cu4O12+y , (0.01 ≤ x ≤ 0.1). According to the XRD patterns the volume fraction of the Bi-2223 phase decreases in favor of Bi-2212. All the samples show normal metallic behavior down to their relevant transition temperature, T c . T c -values decrease significantly with increasing Gd concentration in the system. The hole concentration per Cu has been calculated by using the Presland method and found to decrease with increasing Gd content. The thermoelectric power values of the samples are positive and increase in magnitude with increasing the substitution level. The results obtained have been analyzed in terms of “Two band model with linear T-term” and “Xin’ s two band model”. A very good agreement between the first model and our thermoelectric power data was obtained, but the fit to the second model was poor. The substitution has considerable effect on the thermal conductivity, κ. The magnitude of κ is suppressed and a peak appears just below their T c , values but becomes weaker and broader when the Gd concentration is increased.

15 citations

References
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Journal ArticleDOI
TL;DR: In this paper, annealing results for several Tl-superconductors in the series Tlm(Ba, Sr)2Can−1CunO2n+m+2+δ, for both m=1 and 2, revealing two general results for this class of Bi or TI superconductors: (1) effects on Tc due to labile oxygen occur for all m=2 compounds but are absent in m = 1 compounds with Sr.
Abstract: We have previously shown that Tc for Bi2 (Sr, Ca)n+1CunO2n+4+δ (n=1, 2 and 3) varies with oxygen stoichiometry δ determined by annealing in a variety of oxygen partial pressures and temperatures. Annealing results are now also presented for several Tl-superconductors in the series Tlm(Ba, Sr)2Can−1CunO2n+m+2+δ, for both m=1 and 2, revealing two general results for this class of Bi or TI superconductors: (1) effects on Tc due to labile oxygen occur for all m=2 compounds but are absent in m = 1 compounds with Sr. m=1 compounds with Ba do have variable oxygen but the effects on the c-axis are the opposite to m=2 compounds. This suggests for the latter that the labile oxygen resides in interstitial sites within the Bi2O2 or Tl2O2 bi layers; (2) the hole concentration per Cu decreases in progressing from n = 1 to 2 to 3 in either class so that the parent n = 3 and n = 2 compounds lie respectively on the low- and high-hole concentration sides of the peak in Tc while the n = 1 compounds extend out into the non-superconducting domain at very high hole concentration.

712 citations

Journal ArticleDOI
TL;DR: In this paper, the authors generalize the Heikes formula to include several cases of interacting Fermi systems with spin and show that the high-temperature limit for the thermopower of a system of interacting localized carriers is governed entirely by the entropy change per added carrier.
Abstract: The high-temperature limit for the thermopower of a system of interacting localized carriers is governed entirely by the entropy change per added carrier. The calculation of this quantity reduces to a simple combinatorial problem dependent only on the density of carriers and the interactions stronger than the thermal energy. We have thus been able to generalize the Heikes formula to include several cases of interacting Fermi systems with spin.

515 citations

Journal ArticleDOI
TL;DR: These data are interpreted to demonstrate that the (Cu-O) charge in the sheets largely determines T/sub c/ and that the varying oxygen content and the chains merely provide an insulating reservoir of charge.
Abstract: A series of new $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{y}$-like materials are reported in which the oxygen content and the average [Cu-O] charge (or Cu valence) are separately varied over a wide range. We find a distinct boundary between samples showing anomalous insulating behavior and those with high ${T}_{c}$. These data are interpreted to demonstrate that the [Cu-O] charge in the sheets largely determines ${T}_{c}$ and that the variable oxygen content and the chains merely provide an insulating reservoir of charge.

467 citations

Journal ArticleDOI
01 May 1988-Nature
TL;DR: In this paper, three distinct phases in the homologous series Bi2.1 were identified and indexed on a pseudo-tetragonal subcell with a = b = 5.4 A and c = 24.6 A. The critical temperature for these phases is sharply dependent on the Sr/Ca ratio and oxygen stoichiometry, as determined by heat treatment.
Abstract: Following the report of Maeda et al.1 on high-Tc superconductivity in samples of nominal composition BiSrCaCu2Ox we have identified three distinct phases in the homologous series Bi2.1(Ca, Sr)n+lCunO2n+4+δ with n = 1,2 and 3. These have zero resistance Tcs of 80 K, 91 K and 105 K respectively. The structures in the homologous series appear to be based on alternating double bismuth Bi2O2 layers and perovskite (Sr, Ca)O–CuO2 layers, with higher members obtained by intercalating additional 3.1 A Ca-CuO2 bilayers. The structures can be indexed on a pseudo-tetragonal subcell with a = b = 5.4 A and c = 24.4 A (n = 1), 30.76 A (n = 2) or 36 A (n = 3). We were unable to prepare the n =4 member. In each structure a 2× superlattice structure in the c-direction arises as a natural consequence of a 19/4 incommensurate structure in the b direction, which accounts for 2.1 Bi atoms in the unit formula. The critical temperature, Tc, for these phases is sharply dependent on the Sr/Ca ratio and oxygen stoichiometry, as determined by heat treatment.

271 citations

Journal ArticleDOI
TL;DR: The superconducting properties, magnetic susceptibilities, Hall coefficients, and infrared optical reflection spectra were measured after sufficient characterization of the samples and the antiferromagnetic semiconductor semiconductor normal-metal transition was observed with increasing hole concentration.
Abstract: Polycrystalline samples of ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{Ca}}_{\mathit{n}\mathrm{\ensuremath{-}}1}$${\mathrm{Cu}}_{\mathit{n}}$${\mathrm{O}}_{\mathit{y}}$ with various hole concentrations were synthesized by substituting La for Sr, Y for Ca, and Pb for Bi. The superconducting properties, magnetic susceptibilities, Hall coefficients, and infrared optical reflection spectra were measured after sufficient characterization of the samples. For the n=1 (2:2:0:1) materials, the antiferromagnetic semiconductor--superconductor--normal-metal transition was observed with increasing hole concentration. In n=1 materials the Hall coefficient deviates strongly from the inverse of the hole concentration with increasing hole concentration. On the other hand, in the n=2 (2:2:1:2) materials the Hall coefficient roughly scales with the inverse of hole concentration even for the samples exhibiting superconductivity above liquid-nitrogen temperature. The edge structure in the infrared reflection spectra shifts to higher frequencies with increasing n, whereas it did not change at all when the hole concentration was varied within the same structure (n value). Together with the result of the magnetic-susceptibility measurement, these results are discussed in terms of the several models describing the normal state of high-${\mathit{T}}_{\mathit{c}}$ oxide superconductors.

228 citations