Gh. Ilonca

Effect of Fe substitution on the magnetic and electrical properties of the (Bi1.6Pb0.4)(Sr1.8Ba0.2)Ca2(Cu1−xFex)3Oy superconductor

Abstract The partial substitution of Fe for Cu on the electrical and magnetic properties of (Bi 1.6 Pb 0.4 )(Sr 1.8 Ba 0.2 )Ca 2 (Cu 1− x Fe x ) 3 O y (0 × 0.05) has been investigated by electrical resistance, magnetic a.c. and static susceptibilities measurements. The superconducting transition temperature T c decreases with increasing Fe concentration and the samples are characterized by a linear temperature dependence of the electrical resistance above 2T c . The excess conductivity was analyzed. The inter- and intragrain critical temperatures are affected differently. Static susceptibility yielded the effective magnetic moments corresponding to the high spin state of Fe.

TRANSPORT PROPERTIES AND AC SUSCEPTIBILITIES OF (BI1.6PB0.4)(SR1.8BA0.2)CA2(CU1-XNIX)3OY SUPERCONDUCTOR

The effect of the partial substitution of Cu by Ni in the stabilized 108 K phase was investigated by electrical resistance and a.c. susceptibility measurements. Up to a Ni concentration x = 0.02 the bending of the R (T) curve above Tc can be described in the terms of the Lawrence-Doniach theory. The intergrain and intragrain critical transition temperatures decrease to ∆TCG = 9 K and ∆Tj = 10.9 K respectively by the Ni substitution in the Cu-O pyramids.

Superconducting properties in bulk (Bi1.6Pb0.4)(Sr1.8Ba0.2)Ca2Cu3Oy system

Abstract U(H,T) dependencies for activation energies obtained from Arrhenius plots were well explained by vortex cutting mechanism in an entangled vortex phase. J cJ ( T ) dependencies near T c from χ ″ ( T ) agree with TAPS in the case of SNS-Josephson junctions.

PARACONDUCTIVITY AND HALL EFFECT MEASUREMENTS IN THE SUPERCONDUCTING (BiPb)2(SrBa)2Ca2(Cu1−xCrx)3Oy

The effect of the Cu substitution by Cr in the “2223” superconductor was studied by resistivity and Hall effect measurements. The excess conductivity was analyzed by using the linear and Zou-Anderson extrapolation methods on the electrical resistivity. A crossover temperature is observed only for the x=0 sample. The sheet hole concentration per Cu-site, nHVcell is found to vary linearly with the temperature for all Cr doped samples in the 170–265 K temperature range. Deviations from linearity in the T2 dependence of the inverse Hall mobility above 250 K were evidenced.

Superconducting, magnetic and normal state propeties in bulk (Bi1.6Pb0.4)(Sr1.8Ba0.2)Ca2(Cu1−xCrx)8Oy

Abstract The electrical resistivity, the hole concentration nHV0 per Cu-site, a.c susceptibility and X-ray diffraction for (BiPb)-(SrBa)-(CuCr)-O superconductors has been measured. Near TC paraconductivity studies shows a 2D to 3D crossover in x=0 and only a 2D character in the x ≠ 0 samples. The nHV0 is found to be linear vs. T for all Cr dopped samples. Two subnetworkes with different intergrain coupling strenght were found.

Transport Phenomena in the Mixed and Normal State of (Bi1.6Pb0.4)Sr2Ca2(Cu1-xFex)3Oy Epitaxial Thin Films

We had performed a study on magnetoresistivity, Seebeck, Nernst and Hall effects in the mixed and normal state for Bi2223 thin films in magnetic fields between 0 and 5 T and in the temperature range 5–300 K. The critical temperatures, the Hall concentration, the Nernst and Seebeck coefficients depend strongly on the iron content in the samples. From our experimental data in the mixed state and fluctuation regime, the upper critical field slope (dBc2/dT )=-2:55 T/K was obtained, corresponding to ab-plane coherence length ξab=14 A. The experimental data are in agreement with the predictions of the time-dependent Ginsburg–Landau theory.

Intergranular critical currents and excess conductivity in the Fe-substituted Bi-2223 high Tc superconductor

In this paper me present the effect of iron substitution in the (Bi1.6Pb0,4)(Sr1.88Ba0.2)Ca2(Cu1−xFex)3.1Oy system. From the resistivity and AC susceptibility data we observed that a monotonie decrease of Tc occurs with increasing Fe concentration. A strong reduction of Jc (calculated from AC susceptibility data performed at low magnetic fields in the range 0.4A/m-800A/m) is observed in the doped samples. The crossover temperature from the Anderson-Kim thermally activated flux creep to the thermally activated phase slippage behaviour is depending on the doping concentration. The excess conductivity and 2D-3D crossover is well described by considering Δσ/σ0 as a product of a Gaussian centered at Tc with a Student distribution centered at 2Tc. The alteration of 2D dimensionality above Tc by doping results in the decrease of the number of freedom degrees of the Student distribution.

Thermoelectric and thermomagnetic effects of (B1.6Pb0.4) Sr2Ca2Cu3Ox thin films

Measurements of resistivity, Nernst, Seebeck and Hall effects of Bi 2223 epitaxial thin films for magnetic fields between 0 and 5 T and temperature range 5–300 K are reported.

Superconducting and normal-state transport properties in bulk YBaCuO, doped with Zn

We have investigated the resistivity, the Hall number, n H , and the Hall conductivity, σ H , in bulk YBa 2 (Cu 1-x Zn x ) 3 O 7-δ within the range of Zinc content 0<x<0.06. The magnetic field values were up to 5 T and the temperature range 20 K-300 K. The superconducting transition temperature Tc, as well as, the slope of the normalized resitivity in the normal-state decrease with increasing Zn concentration. The T 3 dependence of σ H -1 , with a change of the slope around 230 K-240 K is correlated with the T-dependence of the carrier concentration

ELECTRICAL AND MAGNETIC PROPERTIES OF BULK (Bi1.6Pb0.4)(Sr1.8Ba0,2)(Ca1-xErx)2Cu3Oy SUPERCONDUCTING SYSTEM

The effects of partial substitution of Ca by Er on the superconductivity and normal state properties of the bulk superconductor (Bi1.6Pb0.4)(Sr1.8Ba0.2)(Ca1-xErx)2Cu3Oy(0≤x≤0.2) have been investigated using electrical resistivity, a.c. and d.c. magnetic susceptibility measurements. Above the excess conductivity region, all samples are characterised by a linear temperature dependence of the electrical resistivity. The analysis of the resistivity data in the normal state reveal that the residual resistivity and the parameter p (related to the percolation path in granular samples) increase with increasing x. The critical transition temperature determined from resistivity data, Tc and Tc(ρ=0), are identical to intra-and intergrain critical temperatures derived from the a.c. susceptibility measurements. These temperatures decreases linearly with increasing Er content. For samples with x≤0.005 a temperature independent susceptibility was evidenced and for x>0.005 the susceptibility data as a function of temperature is well described by a Curie-Weiss law with an effective magnetic moment corresponding to the Er3+ ion.