# Fluctuation-induced excess conductivity in the compounds CaREBaCu3O7−y (RE=La and Sm)

01 Jun 1991-Bulletin of Materials Science (Springer Science and Business Media LLC)-Vol. 14, Iss: 3, pp 747-752

TL;DR: In this article, the authors measured the resistivity of two tetragonal compounds, CaREBaCu3O7−y (RE=La and Sm) at room temperature with T c between 60 and 70 K. The results were analyzed for fluctuation conductivity from 180 K downwards.

Abstract: The compounds CaREBaCu3O7−y (RE=La and Sm) are tetragonal at room temperature withT c between 60 and 70 K. The single-phase compounds were prepared by solid-state reaction. The resistivity was measured by a four-probe technique in a continuous flow cryostat with the temperature being controlled to an accuracy of 10 mK. The resistivity vs temperature showed a break in slope around 180 K in CaLaBaCu3O7−y and around 220 K in CaSmBaCu3O7−y . The results were analysed for fluctuation conductivity from 180 K downwards. A plot of dρ/dT vsT showed a sharp peak atT m =69·69 K for La compound and 66·00 K for the Sm compound. Detailed analysis of the resistivity in the regionT on to 180 K was carried out using the procedure due to Veira and Vidal. The results are discussed in this paper.

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TL;DR: In this article, the authors concluded from detailed investigations on rare-earth-substituted 1113-system CaBaLa 1- x R x Cu 3 O 7- δ (R= Pr, Nd, Sm, Eu, Gd, Er, Ho, Dy, Yb and Tm) that only R=Pr and Nd have a complete range of solid solubility (0⩽ x ⩽ 1.0).

Abstract: It is concluded from detailed investigations on rare-earth-substituted 1113-system CaBaLa 1- x R x Cu 3 O 7- δ (R= Pr, Nd, Sm, Eu, Gd, Er, Ho, Dy, Yb and Tm) that only R=Pr and Nd have a complete range of solid solubility (0⩽ x ⩽1.0). Among other rare-earth ions, only Sm( x ⩽0.8) and Eu( x ⩽0.6) have a large enough range of solid solubility, while the remaining undergo severe phase separation resulting in the formation of multiphase mixtures even for low values of x . The T c -values of CaBaLa 1- x R x Cu 3 O 7- δ (R=Nd, Sm and Eu) show a decreasing trend with increase in x . In these respects, the influence of substitution of rare-earth ions in the CaBaLaCu 3 O 7- δ system is quite different from that in YBa 2 Cu 3 O 7- δ , except that both CaBaPrCu 3 O 7- δ and PrBa 2 Cu 3 O 7- δ are semiconducting.

15 citations

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TL;DR: In this article, resistivity measurements on CaREBaCu 3 O 7− y (RE=La, Sm), Ag coated YBa 2 Cu 3 O7− y, Tl 2 CaBa 2 Ca 2 O 8 and YBa2 Cu 3− x Zn x Cu 3 o 7 − y ( x = 0.05, 0.075 and 0.15) in the paracoherence region.

Abstract: Fluctuations in phase across the weak links in a granular superconductor contribute to the excess conductivity below T m , the temperature at which the plot of temperature derivative of electrical resistivity against temperature shows a maximum. In a narrow range of temperature above T ∞ (the temperature at which the resistivity at which the resistivity becomes zero), the excess conductivity, Δσ = [ σ ( T ) − σ ( T m )], is expected to vary as ( T − T ∞ ) − γ . In this work, resistivity measurements on CaREBaCu 3 O 7− y (RE=La, Sm), Ag coated YBa 2 Cu 3 O 7− y , Tl 2 CaBa 2 Cu 2 O 8 and YBa 2 Cu 3− x Zn x Cu 3 O 7− y ( x =0.05, 0.075, 0.1 and 0.15) in the paracoherence region are reported. Analysis of the data indicates the excess conductivity in this region is better described by the critical exponent y = 1.33. From an analogy between the tunneling Hamiltonian in the granular material and the Hamiltonian for an XY ferromagnet one expects the critical exponent, γ, to be the same as the critical exponent for susceptibility in the ferromangetic case.

6 citations

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TL;DR: The temperature dependence of dc electrical conductivity was measured by two-probe technique in the vicinity of phase transition point for ferroelectrics sodium vanadate and rubidium vanadates doped with different concentrations of La2O3 as discussed by the authors.

Abstract: The temperature dependence of dc electrical conductivity was measured by two-probe technique in the vicinity of phase transition point for ferroelectrics sodium vanadate and rubidium vanadate doped with different concentrations of La2O3. These materials show a sharp change in conductivity at their phase transition temperatures. The results were found to obey the conventional exponential law and the activation energies were calculated for ferroelectric and paraelectric states. It was found that activation energy in ferroelectric phase is smaller than in the paraelectric phase. The activation energy increases slowly with increase in doping concentration of La2O3 up to 0·1 mol%, however, it decreases with further increase in doping concentration, in both ferro and para states. The dc electrical conductivity below the Curie temperature is of mixed type (ionic-electronic) while it is electronic type above the Curie temperature.

1 citations

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TL;DR: In this paper, a rectangular prism with edges in principal crystal directions is prepared with electrodes on the corners of one face, and voltage-current ratios for opposite pairs of electrodes permit calculation of components of the resistivity tensor.

Abstract: A rectangular prism with edges in principal crystal directions is prepared with electrodes on the corners of one face. Voltage‐current ratios for opposite pairs of electrodes permit calculation of components of the resistivity tensor. The method can use small samples, and is best suited to materials describable by two or three tensor components. Examples are given of measurements of V2O3–Cr and oriented amorphous graphite.

574 citations

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Philips

^{1}TL;DR: In this article, a tetragonal bulk superconductor with a T c of 80 K is described, and the standard enthalpy change for the oxidation reaction, Δ H, is determined as 190.4(0.3) kJ⧸mol O 2.

Abstract: The compound CaBaLaCu 3 O 6.9 is a tetragonal bulk superconductor with a T c of 80 K. CaBaLaCu 3 O x is isomorphic to tetragonal YBa 2 Cu 3 O x in which the Ca and La ions are both located at the Y- and Ba-site. High temperature X-ray diffraction and thermogravimetric measurements show no indication for “order-disorder” transitions involving the oxygen ions. TEM micrographs of CaBaLaCu 3 O x show no evidence for a / b twinning. The oxygen content and the partial oxygen pressure of CaBaLaCu 3 O x are determined as a function of temperature. The standard enthalpy change for the oxidation reaction, Δ H , is determined as 190.4(0.3) kJ⧸mol O 2 . Transmission electron diffraction patterns show weak but distinct half-order spots indicating an ordering which can be described by a supercell having axes twice as large as the basic unit cell.

88 citations

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TL;DR: The width of the superconducting transition appears to be a measure of a distance over which layers fluctuate in a correlated manner, consistent with two-dimensional fluctuation theory.

Abstract: Measurements of the in-plane fluctuation-enhanced conductivity of /ital c/-axis oriented Tl-Ba-Ca-Cu-O thin films have been performed over the temperature range /ital T//sub /ital c// to 240 K. The results were consistent with two-dimensional fluctuation theory and with a linear dependence of the normal resistivity on temperature down to (/ital T//minus//ital T//sub /ital c//)/T/sub c/approx.0.03. A crossover to three-dimensional fluctuations close to /ital T//sub /ital c// was not found. The width of the superconducting transition appears to be a measure of a distance over which layers fluctuate in a correlated manner.

67 citations

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TL;DR: In this paper, a simple and unified phenomenological picture of the rounding of the electrical resistivity, ρ(T ), of ceramic HTSC above the critical temperature of individual grains is proposed.

Abstract: A simple and unified phenomenological picture of the rounding of the electrical resistivity, ρ( T ), of ceramic HTSC above the critical temperature of individual grains is proposed. This approach is centered here on the mean-field-like region of Y 1 Ba 2 Cu 3 O 7−δ samples in zero-applied magnetic field. The approach combines the current phenomenological ideas on the electrical conductivity in granular superconductors, together with the empirical features of the Anderson-Zou proposal for the background conductivity, and with the Lawrence-Doniach treatment of the superconducting order parameter fluctuations in layered superconductors. To check this approach we present new experimental data on ρ( T ) in zero-applied magnetic field in different YBCO ceramic compounds, all with the same nominal composition but with important differences in their granular structure. These new experimental data strongly confirm the adequacy of that approach. In particular, the amplitude of the excess conductivity in the mean-field-like region (MFR) is explained quantitatively, to our knowledge for the first time, in ceramic superconductors. Our results also confirm that the paraconductivity in ceramic samples is essentially associated with the in-plane conductivity of the individual grains. Also, our results suggest that in the MFR the critical exponents of the excess conductivity are almost independent of the granular nature of the samples, provided that the correlation length amplitude is smaller than the characteristic dimensions of the grains. In the case of YBCO samples, our results confirm the 3D nature of SCOPF in most of the MFR in zero-applied magnetic field, and for the average amplitude of the Ginzburg-Landau correlation length in the c direction we find, ξ 1 (0) = 2.2 A.

63 citations

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TL;DR: The in-plane paraconductivity in single crystals of YBa/sub 2/Cu/sub 3/O/sub 7/ with exceptionally sharp transitions with good qualitative and some quantitative agreement with the two-dimmensional Aslamazov-Larkin theory is studied.

Abstract: We have studied the in-plane paraconductivity in single crystals of Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ with exceptionally sharp transitions For temperatures greater than \ensuremath{\sim}1 K above the transition temperature ${T}_{c}$, we find good qualitative and some quantitative agreement with the two-dimensional Aslamazov-Larkin theory The jump to zero resistance occurs in a narrow interval of less than 05 K Our data are inconsistent with the Lawrence-Doniach expression for crossover from two to three dimensions

55 citations