We have investigated the effect of Ru substitution on the thermal, structural/microstructural and magnetic properties of Bi-3223 system prepared using solid-state technique. The crystallization studies were made using DSC data with four different uniform heating rates. The formation temperature of Bi-2212 did not change significantly with increasing the Ru concentration; however, it was found that the thermal decomposition temperatures decreased. The activation energy for crystallization, E
 a
 , decreased by increasing the Ru concentration. X-ray diffraction and SEM measurements showed that substitution of Ru for Bi caused significant changes in the crystal structure of the BSCCO material. A distorted and multiphase crystalline structure was observed. The M−−T measurement exhibited that superconducting onset temperature (T
 c
 ) decreased with increasing the Ru concentration in the system. The substitution of Ru for Bi caused the formation of ferromagnetic clusters in the materials, which destroyed the superconductivity in the system. Symmetric M(H) loops were obtained for lower Ru substitution, but in the case of high level substitution of Ru, a typical weak ferromagnetic-like hysteresis loop was found. It is believed that the Ru ions in the system are responsible for ferromagnetic behavior in the highly substituted materials.

The Effect of Ru Substitution on the Thermal, Structural and Magnetic Properties of Bi3Sr2Ca2Cu3Oδ Superconducting System

The influence of calcium substitution at the barium site of porous Y(Ba1-xCax)2Cu3Oδ (x= 0.00, 0.10, 0.20 and 0.30) samples prepared via solid-state reaction method have been investigated. The structure, morphology, critical temperature and critical current were determined by x-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and four-point probe method, respectively. Generally, the curves of normalized resistance for all samples displayed normal metallic behavior above Tc onset. The Tc zero was between 84 K and 71 K with increase in Ca concentration corresponding to a small change of carrier concentration. The critical current density, Jc decreases with increase in Ca concentration. The highest Jc of 2.657 A/cm2 at 50 K was obtained in Ca-free porous YBCO which is higher than that of Ca-free non porous YBCO. Further substitution of Ca at Ba site decreased Jc monotonously. The increase of Ca concentration decreased the volume of unit cell but the crystallographic structure remains in the orthorhombic form where a≠b≠c. The grains are highly compacted and randomly distributed while the grain size decreased as the Ca concentration increased.

Superconducting Properties of Calcium Substitution in Barium Site of Porous YBa2Cu3O7 Ceramics

Sol-gel and solid-state reaction methods were used to synthesize diamond nanoparticles (DNPs) and (DNPs)
 x
 /CuTl-1223 (x = 0, 0.25, 0.50, and 1.00 wt.%) nanoparticle-superconductor composites, respectively. Effects of these DNPs on structural, morphological, compositional, and transport properties of CuTl-1223 superconducting phase were investigated by different experimental techniques such as X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy, scanning electron microscopy (SEM), and resistivity versus temperature (R-T) measurements. The unchanged crystal structure and stoichiometry of host CuTl-1223 superconducting matrix with addition of DNPs gave evidence about the dispersion of nanoparticles at the grain boundaries of the host matrix, which may heal up the inter-granular voids and pores resulting in enhanced inter-grain connectivity. Critical transition temperature T
 c (0) and hole concentration of CuTl-1223 superconductor were observed to be increased with addition of DNPs up to a certain optimum value (i.e. x = 0.5 wt.%).

Study of (DNPs) x /CuTl-1223 Nanoparticle-Superconductor Composites

The effect of Ca substitution by Na, Mg and Yb on the structural and transport properties of Bi1.6Pb0.4Sr2Ca2-xMxCu3Oy (M = Na, Mg and Yb) (x = 0.0 and 0.2) superconducting samples have been investigated. The samples were prepared by the coprecipitation (COP) method. The samples were characterized by x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), electrical resistivity measurement and critical current density. The critical current density (Jc) and transition temperature (Tc zero) of Na, Mg and Yb substituted with x = 0.2 were found to be lower than the pure sample. Tc zero varies between 100 K and 63 K. Mg concentration was found to give the highest Tc zero of 93 K. Tc zero gradually decreased from Mg, Yb to Na corresponding to a small change in the carrier concentration. Jc decreased with Mg, Yb and Na substitution, and it was measured to be 7.4611 A/cm2, 0.0667 A/cm2, 1.4579 A/cm2 and 1.2479 A/cm2 for pure, Na, Mg and Yb substitution, respectively at 60 K. XRD analysis showed that the decrease of the volume fraction for the 2223 phase and increase of the volume fraction for the 2212 phase with substitution of Na, Mg and Yb. The proportion of Bi-2223/Bi-2212 (%) was estimated from 78.13/21.87 for pure to 51.71/48.29 for Na substitution.

Influence of Na, Mg and Yb Substitution for Ca in Bi(Pb)-2223 Superconductor

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Transport and magnetic properties of Bi(Pb)2212 superconducting ceramics doped by low rate of potassium

Samples of stoichiometric composition Bi1.8Pb0.4Sr2−xKxCa2−yNdyCu3Oz with x = 0, 0.01, 0.02, and y = 0, 0.01, 0.02 were prepared by the solid state reaction method. Post-annealing experiments were carried out at 500 °C for 30 h in order to improve the oxygen homogeneity. They were characterized by the x-ray diffraction (XRD) technique, field emission scanning electronic microscopy (FE-SEM), resistivity, magnetization and Raman measurements. The superconducting transition temperature Tczero of the samples varies from 99 to 110 K for different doping. The superconductivity and the critical current density (Jc) of the sample single doped with K are improved compared with the undoped one. We attribute the change of Tc to the variation of carrier concentration. Additionally, the observed change of the normal state resistivity is related not only to carrier concentration but also to the nature of grain boundary links. These analyses are confirmed by Raman and SEM measurements.

Effect of K and Nd substitutions on superconductivity of Bi2223 superconductors

In this work, we extend the scope of the cross derivative of the Gibbs free energy, proposed initially for phase transitions in classical spin models, to the study of the 3rd- and 5th-order Gaussian-type quantum phase transitions in spin-1 XXZ chain with uniaxial and rhombic single-ion anisotropies. These higher-order quantum phase transitions are very diﬃcult to determine by conventional meth-ods. From the cross derivative with respect to the two anisotropic strengths, a single valley structure is observed clearly in each system size. The ﬁnite-size extrapolation of the valley depth shows a perfect logarithmic divergency, signaling the onset of a phase transition therein. Meanwhile, the critical point and the critical exponent for the correlation length are obtained by a power-law ﬁtting of the valley location in each size. The results are in good consistency with best estimations in the literature. The application to other quantum systems with continuous phase transitions is also discussed brieﬂy.

H Y Wu

Papers

Effect of K and Nd substitutions on superconductivity of Bi2223 superconductors

Cross derivative of the Gibbs free energy: for phase transitions in the spin-1 XXZ chain with anisotropies