Introduction of nanoparticles as flux pinning centers in yttrium barium copper oxide (YBCO/Y-123) superconductors has been extensively explored in order to improve high field current-carrying ...capabilities. A uniform distribution of these nanodopants throughout the superconducting matrix is the most essential and desirable. The present work provides a nonconventional approach of introducing nanoparticles into YBCO superconductors by introducing nanoparticles in Y
2
BaCuO
5
(Y-211) preform and then subjecting the preform to infiltration and growth process. The Y-211 preform containing 2 wt.% ceria nanoparticles of the order of 60 nm is referred to as Ce-2 preform. The microstructure of Ce-2 preform shows a uniform distribution of nanoparticles without much interaction even to a temperature of 950 °C. At a higher concentration, a mild interaction was observed which in a way aided in keeping the nanoparticles firmly attached to Y-211 particles. Superconducting transition temperature (
T
c
) of Ce-2 has reduced to 86 from 92 K of pure YBCO with a broad transition. Microstructures of Ce-2 composite suggest strong interaction of ceria nanoparticles with Y-211 as well as with liquid phases which resulted in the formation of fine particles of BaCeO
3
of the order of 200 nm, which has been observed by many investigators. It is possible that some amount of ceria might have entered into a superconducting matrix which can reduce
T
c
as reported earlier. The presence of low
T
c
phase along with a large number of fine particles have improved critical currents densities (
J
c
) to a field of 9 T at 65 K. The present approach has demonstrated substantial improvement in
J
c
at high fields at the expense of low and broad
T
c
. ∖AuthQuery{Q2}{The sentence “The present approach provides a scope for detail study on reaction mechanisms and infiltration process in IGP with nanoparticles” was modified to “The present approach provides a scope for detailed study on reaction mechanisms in infiltration and growth process (IGP) with nanoparticles.” Please check if the edit made appropriately retains the intended meaning of the sentence.}The present approach provides a scope for detailed study on reaction mechanisms in infiltration and growth process (IGP) with nanoparticles.
We report record high current densities of 230 kA cm - 2 at zero field, and in excess of 10 kA cm - 2 up to 7 T at 77 K, in YBa2Cu3O7 - Delta *d (Y-123) superconductors fabricated by a modified ...infiltration growth (IG) process. This was accomplished by optimizing the Y2BaCuO5 (Y-211) preform, into which liquid phases were infiltrated, through a combination of high pressure compaction and limiting the sintering temperature. The optimized sample yielded a Y-123 superconductor with a uniform distribution of fine-grained Y-211. Strong and almost invariant flux pinning observed to high fields up to 7 T, suggest a temperature independent flux pinning mechanism originating from defects in the size range 15--50 nm. Since the present sample has no added grain refiners, nano-sized dopants or mixed rare earths leading to low Tc solid solutions, a unique opportunity presents itself to investigate the cause of the enhanced flux pinning to high fields. We have therefore investigated our samples by transmission electron microscopy, and the studies revealed the presence of domains in the sample with nano-sized defects starting from the domain boundaries, as a possible source of enhanced flux pinning.
The influence of rare earth (RE – Ce, Gd) doping at the Nd site in the NdFeAsO 0.7 F 0.3 superconductor wherein Ce and Gd have ionic radii in the order Ce > Nd > Gd is investigated. The structural ...and superconductivity characterization of the pure and doped samples show that Ce doping enhances the T C of Nd 1−x RE x FeAsO 0.7 F 0.3 to a maximum of 53.6 K at x = 0.1 while Gd doping attains a T C of 55.1 K at x = 0.15. Interestingly, both Ce and Gd doping create neither secondary phases nor precipitates within the detection limit of XRD. However, the lattice defects due to Ce and Gd doping modifies NdFeAsO 0.7 F 0.3 and assists in pinning the flux lines on these defects thereby exhibiting an enhanced J C ( H ) performance especially at high fields. It is also observed that the relatively small ionic size of Gd is more effective in T C enhancement, while the lattice defects due to larger ionic size of Ce favor the remarkable enhancement of J C ( H ).
Doping of non-interacting nanoparticles in YBCO superconductors in order to get fine microstructure defects has been studied. Y-211 inclusion, itself has large potential to create structural defects ...without affecting Y-123 matrix phase. Nanoparticles of grain refining agent like CeO
2
/Pt/PtO
2
are interesting dopants, especially CeO
2
for being cheaper than Pt. POIG process, as is one of the advance processing techniques to get uniform distribution of fine Y-211 particles of the order of 1-2 μm, throughout the YBCO composites. Finer Y-211 particles can drastically increase the pinning centers. Introduction of fine sized CeO
2
as grain refining agent to reduce the size of Y-211 particles would create additional pinning centers. In the present work, the effect of CeO
2
on Y-211size and distribution in POIG processed YBCO composite was studied. It was observed that with increase in CeO
2
content Y-211 particle size decreases below 1μm and even less than 0.5μm for 10 weight percent CeO
2
doping. The mechanism for refinement appears to be the formation of BaCeO
3
on the surface of Y-211 during liquid phase infiltration that leads to splitting of Y-211 into smaller particles.
The origin of high current densities to very high magnetic fields (better than Formula Omitted to 6.5 T at 77 K) in Formula Omitted superconductor fabricated by the preform-optimized ...infiltration-growth process (POIGP) is investigated. The main techniques used in the paper are field-emission scanning electron microscopy and transmission electron microscopy (TEM). An electron-backscattered-diffraction study of the samples is also carried out. A comparison between the microstructures of the optimized sample with the nonoptimized ones show that extensive twinning on a nanometer scale with crossing twins occurring near the optimally separated Formula Omitted precipitates can be the origin of the observed high Formula Omitted in the POIGP sample. The TEM study reveals the presence of very fine defects starting from the twin boundaries. The observed defect spacing and densities account for the uniformly high current densities observed to high fields.
The origin of high current densities to very high magnetic fields (better than 10 3 A · cm -2 to 6.5 T at 77 K) in YBa 2 Cu 3 O 7-δ superconductor fabricated by the preform-optimized ...infiltration-growth process (POIGP) is investigated. The main techniques used in the paper are field-emission scanning electron microscopy and transmission electron microscopy (TEM). An electron-backscattered-diffraction study of the samples is also carried out. A comparison between the microstructures of the optimized sample with the nonoptimized ones show that extensive twinning on a nanometer scale with crossing twins occurring near the optimally separated Y 2 BaCuO 5 precipitates can be the origin of the observed high J c (H) in the POIGP sample. The TEM study reveals the presence of very fine defects starting from the twin boundaries. The observed defect spacing and densities account for the uniformly high current densities observed to high fields.
The effects of rare earth site doping on the structural, superconducting and magnetic properties of SmFeAsO 0.7 F 0.3 iron pnictide are investigated. Gd 3+ and Ce 3+ ions are chosen by virtue of ...their position being on either side of Sm 3+ . Doping of both smaller (Gd 3+ ) and larger (Ce 3+ ) ions at the Sm 3+ site increases the T C up to 55 K. Doping with the smaller Gd 3+ results in lattice contraction and thereby enhances T C . It is interesting to observe that though Ce 3+ doping in SmFeAsO 0.7 F 0.3 exhibits an increase in lattice parameters, a substantial enhancement of T C occurs. The enhancement in T C due to increased charge carrier concentration is also confirmed using Hall Effect measurement. Apart from T C enhancement, the simultaneous doping of both at oxygen and rare earth sites prominently increases the superconducting properties such as J C , H C1 and H C2 . The co-doped samples also exhibit better magnetic field dependence of J C over the entire field of study. It is also observed that the Ce 3+ doped sample shows higher J C in the high field region due to its enhanced flux pinning properties.
The effects of rare earth site doping on the structural, superconducting and magnetic properties of SmFeAsO
0.7
F
0.3
iron pnictide are investigated. Gd
3+
and Ce
3+
ions are chosen by virtue of ...their position being on either side of Sm
3+
. Doping of both smaller (Gd
3+
) and larger (Ce
3+
) ions at the Sm
3+
site increases the
T
C
up to 55 K. Doping with the smaller Gd
3+
results in lattice contraction and thereby enhances
T
C
. It is interesting to observe that though Ce
3+
doping in SmFeAsO
0.7
F
0.3
exhibits an increase in lattice parameters, a substantial enhancement of
T
C
occurs. The enhancement in
T
C
due to increased charge carrier concentration is also confirmed using Hall Effect measurement. Apart from
T
C
enhancement, the simultaneous doping of both at oxygen and rare earth sites prominently increases the superconducting properties such as
J
C
,
H
C1
and
H
C2
. The co-doped samples also exhibit better magnetic field dependence of
J
C
over the entire field of study. It is also observed that the Ce
3+
doped sample shows higher
J
C
in the high field region due to its enhanced flux pinning properties.
The effect of Gd and Ce doping on the structural and transport properties of the (Sm,RE)FeAsO
0.7
F
0.3
superconductor.
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