R. Abd-Shukor

Effects of Fe3O4 Nano Particles Addition in High Temperature Superconductor YBa2Cu3O7-δ

The effects of nano particles Fe3O4 addition on the superconducting and transport properties of YBa2Cu3O7-δ (YBCO) were studied. YBa2Cu3O7-δ superconductor powders were prepared by using high purity oxide powders via solid state reaction method. Nano Fe3O4 with 0.01 – 0.05 wt.% with average size 28 nm was added into YBCO. The transition temperatures (Tc) of the samples were measured by using four point probe method. The critical current (Ic) of the samples has been determined by using the 1 μV/cm criterion from 30 – 77 K. Sample with 0.02 wt.% nano Fe3O4 showed the highest Tc at 87 K. It is interesting to note the same sample also exhibited the highest Jc at 77 K up to 1683 mA/cm2. Nano Fe3O4 has acted as effective flux pinning centers in YBCO. A small amount of nano particles Fe3O4 addition has successfully improved the superconducting and transport properties of YBCO. The excessive addition of nano Fe3O4 (> 0.02 wt.%) suppressed the Tc and Jc. Overall, Jc decreases with increasing temperature (30 – 77 K) as a consequence of thermally activated flux creep. Magnetic impurities normally suppress superconductivity. However, by adding magnetic nano particles, current carrying capacity of superconductors YBCO was enhanced significantly.

Electrical Transport Properties of (Bi1.6Pb0.4Sr2Ca2Cu3O10)/Ag Tapes with Different Nanosized MgO

MgO nanopowders with average size 20 and 40 nm were introduced into (Bi1.6Pb0.4Sr2Ca2Cu3O10)(MgO)x ( wt.%) in the pellet form. The optimum amounts for the highest transport critical current density were and 0.01 wt.% for 20 and 40 nm MgO, respectively. These results were used to fabricate MgO added (Bi, Pb)-2223/Ag sheathed tapes using the powder-in-tube method. The tapes were sintered at 845°C for 50 h and 100 h. The structure, microstructure, and of the tapes were determined. The temperature and magnetic field dependence of for the MgO added tapes exhibited a significant enhancement compared with the nonadded tapes. of 20 nm MgO added tape was higher compared with the 40 nm MgO added tape. A higher was obtained when the tapes were sintered for 100 h. The increase in can be explained as the increase of the flux pinning strength by nanosized MgO. The nanoparticle with size closer to the coherence length was more effective in enhancing .

Effects of nano-sized NiF2 addition in Bi1.4Pb0.6Sr2Ca2Cu3O10+δ superconductor

The effects of NiF2 addition on the superconducting and transport properties of Bi1.4Pb0.6Sr2Ca2Cu3O10+δ (Bi-2223) were studied. Bi-2223 superconductor samples were prepared via conventional nitrate coprecipitation method, and 0.01 wt% - 0.05 wt% of NiF2 nanoparticles with average size of 20 nm were added into the samples. The critical temperature (Tc) of each sample was measured by using the four-point probe method. Furthermore, phase formation and the microstructure of the samples were identified using x-ray diffraction method (XRD) and scanning electron microscope (SEM) respectively. The optimum Tc was observed for the sample with 0.04 wt% addition of NiF2. Results of electrical transport measurement are presented.

Effect of nanoparticles with different size on the transport critical current density of Bi1.6Pb0.4Sr2Ca2Cu3O10 superconductor

In general, for a nanoparticle to act as a pinning center, the size L should be larger than the coherence length, x and smaller than the penetration depth, λ. In this paper we compared the effects of different nano-sized particles (where x < L < λ), MgO (20 and 40 nm) versus ZnO (6 and 30 nm) on the transport critical current density of the Bi-based superconductors. All nanoparticle added samples showed higher transport critical current density, Jc compared with the non-added samples. In Bi1.6Pb0.4Sr2Ca2Cu3O10(MgO)x, the 20 nm MgO added samples showed a higher Jc compared with the 40 nm MgO added samples. The 6 nm ZnO added samples also showed higher Jc compared to the 30 nm added samples. These results showed that the size of flux pinning center is important in enhancing Jc and particle with size closer to the coherence length showed higher transport critical current density.

Oxygen related ultrasonic attenuation and elastic anomalies in EuBa2Cu3O7-δ (δ∼0.02 and 0.45)

Abstract Ultrasonic shear velocity and attenuation measurements on superconducting ( δ ∼0.02) and non-superconducting ( δ ∼0.45) polycrystalline EuBa 2 Cu 3 O 7- δ have been performed at 7-8 MHz between 80 K and 220 K. Enhanced attenuation and softening tendency was observed near 170 K in the superconducting material. The attenuation peak is greatly suppressed and no softening tendency was observed in the non-superconducting sample. The reduction of oxygen content from O 6.98 to O 6.55 caused the absolute shear velocity to decrease. The O 6.98 sample showed a 2.25% change in shear velocity between 80 K and 220 K while the O 6.55 sample showed a 3.75% change within the same temperature range. These anomalies are discussed in terms of possible oxygen ordering. The acoustic Debye temperature of the superconducting sample in the void-free approximation is estimated to be Θ D ∼457 K.

Enhanced Transport Critical Current Density of NiO Nano Particles Added YBCO Superconductors

The effects of NiO nanoparticles addition in YBa2Cu3O7-δ (YBCO) superconductors had been investigated. YBCO superconductor powders were prepared by using high purity oxide powders via solid state reaction method. 0.01 0.05 wt.% of NiO nanoparticles were added into YBCO. The critical temperature (Tc) and transport critical current density (Jc) were determined by using four point probe method. The lattice parameters and morphology of the samples were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM), respectively. Tc of YBCO increased from 84 K to 87 K with 0.02 wt.% of NiO nanoparticles addition. The addition on NiO nanoparticles have significantly enhanced transport critical current density of YBCO by acting as flux pinning centers. YBCO with 0.03 wt.% of NiO nanoparticles performed the highest Jcup to 1265 mA/cm2 among the NiO-added samples. However, excessive addition of NiO nanoparticles in YBCO caused degradation in Tc and Jc.

Effect of Hf substitutions on the formation and superconductivity of Tl-1212 type phase TlSr2(Ca1−xHfx)Cu2O7−δ

The TlSr2(Ca1−xHfx)Cu2O7−δ (Tl-1212) superconductor for x = 0.0 to 0.4 has been prepared by the solid state reaction method and studied by powder X-ray diffraction method, electrical resistance and scanning electron microscope (SEM). Most of the samples showed the Tl-1212 as the major phase and Tl-1201 as the minor phases. Small amounts of Hf-substitution (x ≤ 0.15 or x ≤ 0.25) maintained the formation of the Tl-1212 phase but larger amounts led to the formation of 1201 and an unknown impurity phase. The resistance versus temperature curve showed metallic behavior for all samples. The resistance versus temperature curves showed onset transition temperature (Tc onset) between 38 and 47 K for Hf substitution.

Transport critical current density of Bi-Sr-Ca-Cu-O/Ag superconductor tapes with addition of Fe3O4 as flux pinning center

This paper reports on the flux pinning capability of micron size Fe3O4 in Bi-Sr-Ca-Cu-O superconductor tapes. Ag sheathed high temperature superconductor tapes with starting compositions (Bi,Pb)2Sr2Ca2Cu3O10 (2223) and (Bi,Pb)2Sr2Ca2Cu3O10-(Fe3O4)0.01 were fabricated using the powder in tube method. The Bi-Sr-Ca-Cu-O powders were prepared by using the co-precipitation technique. The effects of Fe3O4 addition on the microstructure, phase formation, critical temperature and transport critical current density, Jc were studied. The Jc value of the Fe3O4added tapes is higher (6,090 A/cm2 at 77 K and 24,500 A/cm2 at 30 K, in zero field) than the non-added tapes (3,730 A/cm2 at 77 K and 13,3180 A/cm2 at 30 K, in zero field). A sudden decrease of Jc in low magnetic fields (B < 0.12 T) when applied parallel (B∥) and perpendicular (B⊥) to the tapes surface was observed. The destruction of weak links played an important role in the early Jc suppression. The rate of decrease of Jc was observed to decrease when the magnetic field was increased further. Improvement in the flux pinning was observed in (Bi, Pb)2Sr2Ca2Cu3O10-(Fe3O4)0.01 tapes. This study shows that magnetic particles such as Fe3O4 can act as effective pinning centers leading to the enhancement of Jc in the system.

Superconducting and elastic properties of (Dy1−xPrx)BaSrCu3O7−δ

Pr-substituted (Dy1−xPrx)BaSrCu3O7−δ (x=0.0, 0.1, 0.2, 0.4 and 0.7) has been investigated for its superconducting and elastic properties. Structural transition from orthorhombic to tetragonal symmetry is observed at x=0.1. Temperature-dependent sound velocity was measured using the pulse-echo overlap method. Elastic anomalies in the form of lattice stiffening with decreasing temperature were observed above 200 K. These anomalies were attributed to oxygen vacancy orderings in the Cu(1)O plane and also depended on the configurational state of oxygen orderings which is strongly influenced by Pr-doping.

Electrical Properties of Li Substituted (Tl0.85Cr0.15)Sr2-x Li x CaCu2O7 Superconductor

The effects of Li substitution for Sr in (Tl0.85Cr0.15)Sr2-x Li x CaCu2O7 (Tl-1212) with x = 0 - 0.10 were investigated. Tl-1212 superconductor pellets were prepared via solid-state reaction and precursor method. The samples were characterized by x-ray diffraction and four-point probe methods. The XRD patterns showed that all samples formed mixed phases of Tl-1212 and Ca0.3Sr0.7CuO2 (CSCO). The temperature-dependent resistance measurements showed metallic-behavior for all samples with onset transition temperature, T c onset between 96 K and 105 K and zero resistance temperature, T c zero between 85 K and 94 K. The transition-width, ΔTc of all samples was in the range of 4 K to 11 K. The x = 0.02 and 0.07 sample showed increase in Tc onset to 105 K and 102 K, respectively. This work showed that Li improved the transition temperature for x = 0.02 and 0.07 samples although the dominant phase was not Tl-1212.