Decebal Ciurchea

Effect of Fe substitution for Cu in the mixed state of (Bi, Pb):2223 superconductor

The effect of the partial substitution of x = 0.02 Fe for Cu in the stabilized (Bi, Pb):2223 phase has been investigated by magnetoresistivity measurements up to 0.7 T. The intra- and intergranular transitions as a function of magnetic field were analysed using versus T curves. The Arrhenius plots are represented by a family of straight lines. The activation energy is proportional to . The main dissipation process is related to the vortex cutting mechanism.

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.

AC susceptibility study of the inter- and intragranular properties in (Bi,Pb):2223 superconductor

The temperature and amplitude of AC field dependencies of both inter-and intragranular Tp and Tg temperatures of the imaginary peaks of χ′′ has been studied for a sintered single phase (Bi,Pb):2223 superconductor. The AC field dependencies for Tp and Tg and the relation between inter- and intragrain force densities were discussed by using Muller critical-state model. From the χ′′(T) curve, the values of intergrain magnetic critical current density JcJ was obtained via the application of Beans critical state model. JcJ(T) dependence near Tc agree with the assumption of SNS intergrain junctions.

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.

Effects of Y, Er and Lu substitution upon superconductivity in (Bi,Pb):2223 system

Abstract The effect of partial substitution of Ca by x=0.02Y, 0.02Er and 0.02Lu in the (Bi,Pb):2223 superconductor was investigated by resistivity and AC susceptibility measurements. The rate of depression for Tc in x=0.02 samples is found to be almost the same for all substituents. Residual resistivity varies according to the type of substituting ions. The linear dependence of intergranular temperature Tp as a function of AC field amplitude agrees with Muller critical state model.

Transport properties of YBa2(Cu1-xZnx)3O7- delta films

Zn doped epitaxial films of YBa2(Cu1-xZnx)3O7- delta with 0<or=x<or=0.06 have been prepared by high-oxygen-pressure d.c. sputtering from stoichiometric targets on MgO substrate. The temperature dependences of the transport properties were investigated by electrical resistivity and Hall effect measurements. The transition temperatures and the Hall concentration per unit cell decrease with increasing Zn content. The temperature dependence of the Hall density nH and T2 dependence of the inverse mobility shows an anomaly around 250 K.

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.

Statistical representation of the excess conductivity in a Bi-Sr-Ca-Cu-O superconductor

The onset of superconductivity may be described by the product of a Gaussian with a Student distribution. The excess conductivity properties of many specimens are numerically fitted and prove the accuracy of this model. The number of degrees of freedom yielded by the Student distribution corresponds to the number of independent variants of percolation of the Cooper pairs above . This number depends linearly on the type of 3d substituents of Cu (Zn, Fe, Ni).

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.