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Many new superconducting materials have been discovered in recent years. This includes hydrogen sulfide which superconducts at 203 K under high pressure and Fe-As based materials. To this date the copper oxide-based materials remain as the highest transition temperature superconductor under normal pressure. In this paper we discuss the use of nano-sized particle as pinning center in the Ag-sheathed high temperature superconductor tapes to enhance the transport properties. When the size d of the pinning center is between the coherence length ξ and the penetration depth λ (ξ < d < λ), a stronger interaction between the pinning center and flux lines leading to higher transport critical current density, Jc can be expected. The effect of nanoparticle with size between the coherence length and the penetration depth i.e. ξ < d < λ, Co3O4 on superconductor tapes is discussed in this paper. Three types of Bi(Pb)-Sr-Ca-Cu-O starting materials namely from co-precipitation method without Co3O4 and with 30 nm and 50 nm Co3O4 addition have been prepared. The composition of the 30 nm and 50 nm Co3O4 added samples is (Bi1.6Pb0.4)Sr2Ca2Cu3O10-(Co3O4)0.02 and (Bi1.6Pb0.4)Sr2Ca2Cu3O10 -(Co3O4)0.01, respectively. The tapes (~2-3 cm long) were heated at 845oC for 100 and 150 h. All nanoparticles added tapes showed higher Jc compared to the non-added tapes. By comparing the current results with our previously reported results, the tapes with 30 nm Co3O4 sintered for 50 h showed the highest Jc at all temperatures. This work also showed that smaller magnetic nanoparticles enhanced Jc better than larger particles, A longer sintering time (> 50 h) degraded Jc. [ABSTRACT FROM AUTHOR]

The effect of Pb substitution on Tl-1212 high Tc superconductor with nominal starting composition (Tl1-xPbx)Sr2CaCu2O7-δ (x = 0.1 - 0.7) has been investigated. Nano-sized PbO (10-30 nm) was used as a starting component. The samples were synthesized using the solid-state reaction technique and studied by powder X-ray diffraction method, electrical resistance measurements and scanning electron microscopy. The resistance-temperature curves showed metallic behavior for all samples. Samples with x = 0.6 showed the highest Tc onset (89 K) and Tc zero (78 K). This sample also showed the highest peak temperature for the derivative of the resistivity (ρ) versus temperature (T) curve, dρ/dT = 85 K. The X-ray diffraction patterns showed a major Tl-1212 phase with few weak diffraction lines of the Tl-1201. The deviation of electrical resistivity from linear behavior near the transition temperature was explained in terms of excess conductivity associated with Cooper pair formation. This work showed that nano-sized PbO could be used to enhance the formation of the superconducting Tl-1212 phase. [ABSTRACT FROM AUTHOR]

The effect of 0.01 wt. % Co0.5Zn0.5Fe2O4 (CZFO) and Ni0.5 Zn0.5 Fe2 O4 (NZFO) nanoparticles on (Bi1.6 Pb0.4)Sr2Ca2Cu3 O10 (Bi2223) was investigated. Ultrafine Bi-2223 superconductor powders were produced by using the co-precipitation method. XRD analysis showed that the volume fraction of (Bi1.6 Pb0.4)Sr2Ca2Cu3 O10 increased when CZFO and NZFO was added. No peaks from CZFO and NZFO were detected from the XRD patterns. The transition temperature was measured by using electrical resistance (Tc) and AC susceptibility (Tcχ) versus temperature measurements. The transition temperature from resistance measurements showed slight decrease as the complex magnetic oxides nanoparticle were added into the samples. However the AC susceptibility measurements showed two distinct transitions indicating the presence of the Bi-2223 and Bi-2212 phase in all samples. [ABSTRACT FROM AUTHOR]

The effects of nano-sized Co0.5Ni0.5Fe2O4 addition on the superconducting and transport properties of Bi1.6Pb0.4Sr2Ca2Cu3O10 (Bi-2223) in bulk form has been investigated. Bi-2223 superconductor was fabricated using coprecipitation method and 0.01 - 0.05 wt% of Co0.5Ni0.5Fe2O4 nanoparticles with average size of 20 nm were added into the samples. The critical temperature (Tc) and critical current density (Jc) of the samples were measured by using the four-point probe method, while the phase formation and microstructure of the samples were examined using x-ray diffraction and SEM respectively. It was found that Jc of all samples added with Co0.5Ni0.5Fe2O4 were higher than nonadded sample, with x = 0.01 wt. % sample showing the highest Jc. This study showed that small addition of nano-Co0.5Ni0.5Fe2O4 can effectively enhance the transport critical current density in Bi-2223 superconductor. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The effect of nano-sized Co3O4 (10 - 30 nm) addition on YBa2Cu3O7-δ(Co3O4)x with x = 0 to 0.12 wt.% has been investigated by powder X-ray diffraction method, dc electrical resistance measurements and scanning electron microscopy. The Co3O4 particle size was larger than the coherence length but smaller than the penetration depth of the YBa2Cu3O7-δ superconductor. The onset transition temperature (Tc onset) showed no significant changes for low Co3O4 addition (x ≤ 0.02 wt. %) and then decreased monotonically with the increase in Co3O4 content indicating a pair-breaking like mechanism in Tc suppression for x = 0.03 to 0.12 wt. %. A sudden broadening of the superconducting-transitionwidth for x ≥ 0.11 wt. % was also observed. The transport properties were measured and related to the microstructure. Scanning electron micrographs showed homogeneous distribution of Co3O4 throughout the samples and the distance between particles was smaller than 1 μm but larger than the typical Abrikosov vortex lattice constant. [ABSTRACT FROM AUTHOR]

The effect of nano-sized Co3O4 (10 - 30 nm) addition on YBa2Cu3O7-δ(Co3O4)x with x = 0 to 0.12 wt.% has been investigated by powder X-ray diffraction method, dc electrical resistance measurements and scanning electron microscopy. The Co3O4 particle size was larger than the coherence length but smaller than the penetration depth of the YBa2Cu3O7-δ superconductor. The onset transition temperature (Tc onset) showed no significant changes for low Co3O4 addition (x ≤ 0.02 wt. %) and then decreased monotonically with the increase in Co3O4 content indicating a pair-breaking like mechanism in Tc suppression for x = 0.03 to 0.12 wt. %. A sudden broadening of the superconducting-transitionwidth for x ≥ 0.11 wt. % was also observed. The transport properties were measured and related to the microstructure. Scanning electron micrographs showed homogeneous distribution of Co3O4 throughout the samples and the distance between particles was smaller than 1 μm but larger than the typical Abrikosov vortex lattice constant. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The effect of nanosized PbO additions on the superconducting properties of (Bi, Pb)-2223(PbO)x (x = 0 - 0.15 wt. %) prepared by the co-precipitation method was studied. The structure and the microstructure of samples were examined by powder XRD and SEM, respectively. The transport critical current density (Jc), onset transition temperature (Jc onset) and zero resistance temperature (Jc zero) were determined by using four-probe method. It was observed that PbO additions enhanced Jc for all added samples. The x = 0.05 wt. % sample showed the highest Jc (19.3 and 11.3 A/cm² at 30 and 77 K, respectively) This study showed that the addition of PbO, as a result of existence of the effective artificial pinning, provided extra flux pinning centers in the (Bi, Pb)-2223 superconductor. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Nanosized Cr2O3 (6 nm) has been introduced into (Bi,Pb)-Sr-Ca-Cu-O/Ag tapes fabricated by the powderin-tube method. The starting powder with composition (Bi,Pb)2Sr2Ca2Cu3O10(Cr2O3)0.05 was prepared by the solid state reaction method. The superconductor tapes with thickness of about 0.3 mm and length about 2 cm were heated at 845°C for 96, 144, 192 and 240 h. The samples were characterized by the four point probe electrical measurements, X-ray powder diffraction method and scanning electron microscopy. The transport critical current density, Jc was measured from 30 to 65 K using the 1 μ/cm criterion. The highest Jc was obtained for the tape heated for 240 h with Jc = 1700 A/cm2 at 30 K. XRD patterns showed that the samples consisted of the 2212 and 2223 phase. SEM micrographs showed the plat-like structure. The role of nano-Cr2O3 in the superconductor system is discussed. The size of the nanoparticle (R) was larger than the coherence length, ξ but smaller than the penetration depth, λ(ξ< R <λ). The temperature dependent Jc from 30 to 65 K showed a linear relation for all except for the tapes heated at 240 h. Using the self-field approximation together with the Jc dependence on temperature, it was observed that between 30 and 65 K the characteristic length (Lc) associated with the pinning force Fp is approximately the same as the average grain size (Rg) in all samples except for the tapes heated for 240 h where Rg < Lc. This shows that a change in the flux pinning mechanism occurred in the tapes when the heating time was prolonged. [ABSTRACT FROM AUTHOR]

The objective of this study is to investigate the effect of nano Co3O4 addition in Bi(Pb)-Sr-Ca-Cu-O superconductor on the critical temperature (TC), the phase formation and the microstructure. Two kinds of precursor powder were studied; one was a pure Bi(Pb)-Sr-Ca-Cu-O and the other was a mixture of Bi(Pb)-Sr-Ca-Cu-O with nano Co3O4 powder. The precursors were prepared by the conventional powder solid-state reaction. 0.01 wt% to 0.04 wt% of nano-particles of Co3O4 was added to the samples. Co3O4 act as the magnetic impurities in the superconductor system. From the results, it showed that a low concentration and appropriate amount of magnetic impurities enhanced the critical temperature of Bi(Pb)-Sr-Ca-Cu-O superconductor. The materials contained both the high Tc phase (Bi2Sr2Ca2Cu3OX) and the low Tc phase (Bi2Sr2Ca2Cu3OX). [ABSTRACT FROM AUTHOR]

This paper discusses the enhancement of transport current density in Bi-Sr-Ca-Cu-O tapes with nano g-Fe2O3 as flux pinning center. Intermediate rolling also enhanced the transport current density in this system. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]