MgB 2 /Fe wires with 10 at. % excess Mg produced by in situ powder-in-tube processing werecompared to normal stoichiometric MgB 2 /Fe wires prepared by the same method. It was found thatthe critical current density J c and the irreversibility field (H irr) were significantly enhanced forMgB 2 /Fe wires with excess Mg. The transport J c for 10 at. % Mg excess samples sintered at 800 degrees C, measured at a field of up to 14 T, increased by a factor of 2 compared to that for the normal MgB 2 wires. The best J c results for the 10 at. % Mg excess sample were obtained by heating thesample at 600 degrees C for 1 h; the J c at a field of 8 T and at temperature of 10 K reached 3104 A/cm2. The detailed analysis of the effect of excess Mg on the microstructures, the J c , andthe H irr , of MgB 2 /Fe wires are presented in this paper.
Pure MgB2
bulk samples were sintered in different atmospheres: high purity Ar, high purity Ar with
0.01% O2, high purity Ar
with 0.03% O2 and high
purity Ar with 5% H2. The superconductivity and microstructure of these samples were studied. It
was found that in the range of this study the impurity gas in Ar had strong
effects on aspects of the superconductivity such as critical current density,
Jc, the irreversibility
field, Hirr, and the
upper critical field Hc2. When the samples were sintered in Ar with
O2 impurity, their low
field Jc decreased as the
O2 content increased.
The high field Jc, in contrast, was improved as the concentration of the
O2
impurity increased. For the sample sintered in Ar with
H2 impurity,
its Jc
is significantly higher than that of the sample sintered in high purity Ar. The smaller grain size and
crystallinity degradation caused by the impure atmosphere is proposed to be the reason for the
Jc improvement
in both the O2
and the H2
added to the Ar gas sintering cases.
The influence of water pressure in the metal–organic deposition (MOD) method on the texture and morphology
of YBa2Cu3O7−X
(YBCO) films grown on buffered metal substrates was investigated. The water pressure was
varied from 4.2% to 10.0%, with the other process parameters, such as annealing temperature
and oxygen pressure, kept constant. In this work, a YBCO precursor solution was prepared
using a fluorine-free Y and Cu precursor solution with the addition of Sm. MOD-YBCO
films were fabricated by continuous slot-die coating and calcination, followed by high
temperature annealing. Using x-ray diffraction analysis, unreacted phase peaks, such as
BaF2
peaks, were found in the samples made at a water pressure of 4.2%; however, the
BaF2
peak intensity was much reduced as the water pressure was increased. The higher water
pressure of about 10.0% in this experiment led to the poor crystallinity of MOD-YBCO
films, possibly due to the fast reaction with the supplied water vapor. Meanwhile, the
morphologies of the YBCO films were not much different from each other in the
range of water pressure of this work. The maximum critical current density of
3.8 MA cm−2
was obtained when the sample was made at the water pressure of 6.2% and the annealing temperature
of 780 °C.
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