426 research outputs found
Fabrication of high performance MgB2 wires by an internal Mg diffusion process
We succeeded in the fabrication of high-Jc MgB2/Fe wires applying the
internal Mg diffusion (IMD) process with pure Mg core and SiC addition. A pure
Mg rod with 2 mm diameter was placed at the center of a Fe tube, and the space
between Mg and Fe tube was filled with B powder or the powder mixture of
B-(5mol%)SiC. The composite was cold worked into 1.2mm diameter wire and
finally heat treated at temperatures above the melting point of Mg(~650oC).
During the heat treatment liquid Mg infiltrated into B layer and reacted with B
to form MgB2. X-ray diffraction analysis indicated that the major phase in the
reacted layer is MgB2. SEM analysis shows that the density of MgB2 layer is
higher than that of usual powder-in-tube(PIT) processed wires. The wires with
5mol% SiC addition heat treated at 670oC showed Jc values higher than 105A/cm2
in 8T and 41,000A/cm2 in 10T at 4.2K. These values are much higher than those
of usual PIT processed wires even compared to the ones with SiC addition.
Higher density of MgB2 layer obtained by the diffusion reaction is the major
cause of this excellent Jc values.Comment: 7page, 6figure
A Penetration Depth Study on Li2Pd3B and Li2Pt3B
In this paper we present a penetration depth study on the newly discovered
superconductors LiPdB and LiPtB. Surprisingly, the
low-temperature penetration depth demonstrates distinct behavior in
these two isostructural compounds. In LiPdB, follows an
exponential decay and can be nicely fitted by a two-gap BCS superconducting
model with a small gap K and a large gap K.
However, linear temperature dependence of is observed in LiPtB
below 0.3, giving evidence of line nodes in the energy gap.Comment: 2 pages, submitted to LT2
Superconductivity in metal rich Li-Pd-B ternary Boride
8K superconductivity was observed in the metal rich Li-Pd-B ternary system.
Structural, microstructural, electrical and magnetic investigations for various
compositions proved that Li2Pd3B compound, which has a cubic structure composed
of distorted Pd6B octahedrons, is responsible for the superconductivity. This
is the first observation of superconductivity in metal rich ternary borides
containing alkaline metal and Pd as a late transition metal. The compound
prepared by arc melting has high density, is stable in the air and has an upper
critical field, Hc2(0), of 6T.Comment: 4 pages, 5 figur
Discovery of Li2(Pd,Pt)3B superconductors
Critical temperature Tc of the Li2(Pd1-xPtx)3B was reported to be 7-8K for
x=0 and 2.2-2.8K for x=1. In this article we present our preliminary results on
behavior of magnetization-temperature curves with starting composition of Pd-B
precursor, y-Li concentration in LiyPd3B and post-annealing of the Pd-end
compound. Results suggest that to maximize Tc ratio Pd:B should be close to
3:1, while y-Li has to be optimum. The lowest Tc for LiyPd3B was 4.4-4.6K,
while post-annealings at 560 deg. C allowed enhancement of Tc up to 8.2-8.4K.
Compositions Li2Z3B with Z=Ni, Ru, Rh, Re, Ag are not superconducting down to
1.8K. Exception is composition with Re showing superconductivity due to Re3B
compound. All samples were prepared by arc melting.Comment: 6 pages, 5 figs. presented at M2S, 200
Strain Effect in MgB2/Stainless Steel Superconducting Tape
The influence of mechanical strain on the critical current (Ic) is
investigated for MgB2/stainless steel (SUS316) superconducting tapes. The tapes
are fabricated by using 'powder in tube' method and deformation process without
any heat treatment. The tensile axial strain along tape length is successfully
induced to the sample by using a U-shape holder made of stainless steel
(SUS304). Two samples are examined at 4.2 K in 5 T (B is applied perpendicular
to the tape surface). While the initial Ic at zero external strain state (Ic0)
varies (30.4 and 33.3 A), normalized Ic (Ic/Ic0) vs. external strain relations
fall on the same curve. Linear increase of Ic is observed from zero external
strain state to 0.5% strain (107% of Ic0). Rapid and large degradation occurs
at the strain exceeding 0.4-0.5%. High durability against stress can be
expected for MgB2/stainless steel superconducting tapes.Comment: 3 pages including 2 figures, submitted to Physica
Landau and Ott scaling for the kinetic energy density and the low conventional superconductors, and Nb
The scaling approach recently proposed by Landau and Ott for isothermal
magnetization curves is extended to the average kinetic energy density of the
condensate. Two low superconductors, Nb and are studied
and their isothermal reversible magnetization shown to display Landau and Ott
scaling. Good agreement is obtained for the upper critical field ,
determined from the Abrikosov approximation for the reversible region (standard
linear extrapolation of the magnetization curve), and from the maximum of the
kinetic energy curves. For the full range of data, which includes the
irreversible region, the isothermal curves for show an
impressive collapse into a single curve over the entire range of field
measurements. The Nb isothermal curves exhibit the interesting
feature of a constant and temperature independent minimum value
High transport critical current density obtained for Powder-In-Tube-processed MgB2 tapes and wires using stainless steel and Cu-Ni tubes
MgB2 tapes and wires were fabricated by the Powder-In-Tube method. Stainless
steel and Cu-Ni tubes were used as sheath materials, and no heat treatment was
applied. The tapes made of stainless steel showed transport critical current
density Jc of about 10,000A/cm2 at 4.2K and 5T. A high Jc of about 300,000A/cm2
was obtained by extrapolating the Jc-B curves to zero field.
Multifilamentary(7-core) MgB2 wire was successfully fabricated using Cu-Ni
tubes. For both tapes and wires the grain connectivity of MgB2 was as good as a
high-pressure sintered bulk sample. However, the Jc of the Cu-Ni sheathed wire
was lower than the stainless steel sheathed tape due to the lower packing
density of MgB2.Comment: 4 pages, 3 figure
Superconducting Properties of MgB2 Bulk Materials Prepared by High Pressure Sintering
High-density bulk materials of a newly discovered 40K intermetallic MgB2
superconductor were prepared by high pressure sintering. Superconducting
transition with the onset temperature of 39K was confirmed by both magnetic and
resistive measurements. Magnetization versus field (M-H) curve shows the
behavior of a typical Type II superconductor and the lower critical field
Hc1(0) estimated from M-H curve is 0.032T. The bulk sample shows good
connection between grains and critical current density Jc estimated from the
magnetization hysteresis using sample size was 2x104A/cm2 at 20K and 1T. Upper
critical field Hc2(0) determined by extrapolating the onset of resistive
transition and assuming a dirty limit is 18T.Comment: 3Pages PD
Muon-spin-rotation measurements of the penetration depth in Li_2Pd_3B
Measurements of the magnetic field penetration depth in the ternary
boride superconductor LiPdB ( K) have been carried out by
means of muon-spin rotation (SR). The absolute values of , the
Ginzburg-Landau parameter , and the first and the second
critical fields at T=0 obtained from SR were found to be
nm, , mT, and
T, respectively. The zero-temperature value of the
superconducting gap 1.31(3) meV was found, corresponding to the
ratio . At low temperatures saturates and
becomes constant below , in agreement with what is expected for
s-wave BCS superconductors. Our results suggest that LiPdB is a s-wave
BCS superconductor with the only one isotropic energy gap.Comment: 6 pages, 7 figure
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