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Discovery of superconductivity in Fe-based cuprates
PHYSICA® ELSEVIER
Physica C 341-348 (2000) 563-564
www.elsevier.nl/Iocate/physc
Discovery of Superconductivity in Fe-Based Cuprates J. Shimoyama, K. Otzschi, T. Hinouchi and K. Kishio Department of Superconductivity, University of Tokyo 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan The Fe-based cuprates, FeSr2YCu2Oy[Fe1212] and relating compounds were found to exhibit superconductivity with Te(onset) up to 62K. Additional annealing process under moderately reducing atmosphere is believed to be crucial for suppression of site exchange between Fe and Cu, resulting in the new superconducting system.
showed discontinuity between y=7.2 and 7.5
1. INTRODUCTION
similarly in the case of SrFeO3.8, while y changed Partial substitution of high-valence metals, such
continuously
in the conventional
phase
with
as Fe, Re, W, ..., for Cu to the so-called chain site,
temperature and P(O2).
Cu(1), has been known to be effective for stabilizing
exchange between Fe and Cu occurred in the
YSr2Cu3Oy phase. In particular, Fe can fully
conventional
substitute Cu(1) site, however, the superconductivity
superconductivity
has been reported only in a narrow compositional
eliminated by annealing under moderately reducing
range of x=0.3~0.4 in
(CUl.xFex)YSr2Cu20y[1].
phase,
This suggested that the site which
of Fe1212,
might
suppress
and it can be
conditions.
Disappearance of superconductivity in higher Fe
In the present study, we have attempted to make
concentration, x>0.5, was believed to be due to the
the Fe1212 compounds to be new superconductors
insufficient hole carrier concentration in the material.
by applying the reducing process prior to the
In our preliminary study on the themogravimetry
oxygenation annealing.
performed for FeSr2YCu2Oy [Fe1212], behaviors of the
oxygen nonstoichiometry in the
Fe1212
2. EXPERIMENTAL
dramatically changed after holding under moderately
Sintered bulk samples of FeSr2YCu2Oy were
reducing conditions, -1073K and P(O2)=102pa.
synthesized by conventional solid state reaction
The new phase was confirmed to maintain the
starting from high purity powders of Fe203, SrCO3,
original Fe1212 structure without significant change
Y203 and CuO. Powder mixture was calcined at
in its lattice constants. Oxygen nonstoichiometry of the new phase
1173K for 12h and sintered at 1223K over 24h in air. The resulting samples were annealed at -1073K
0921-4534/00/$ - see front matter @ 2000 Elsevier Science B.V PII S0921-4534(00)00593-1
All rights reserved.
J. Shimoyama et al./Physica C 341-348 (2000) 563-564
564
under flowing a reducing gas with P(O2) = 102pa for 5h, then cooled down to 573K and changed atmosphere to P(O2)=105Pa.
Finally, high pressure
oxygen annealing, at 523K in P(O2)=3.5 x 107pa for 24h,
was
performed.
Samples
with
compositions of FeSr2(Y,Ca)Cu2Oy
and zero resistance was attained at 25K. Samples of FeSr2(Y0.9Cao.1)Cu2Oy also showed superconductivity, however, Tc was not improved further.
nominal
were also
synthesized in a similar way.
4. CONCLUSIONS The Fe1212 compounds were found to show superconductivity by applying annealing process
3. RESULTS AND DISCUSSIONS
under moderately reducing conditions, which is
The Fe1212 samples prepared without reducing annealing process did not show any sign of
believed to suppress incorporation of Fe to the CuO2-plane in the present system,
superconductivity even after the high pressure oxygen annealing, which increased y to 7.64.
On
the other hand, the samples annealed under
ACKNOWLEDGEMENT This work was partially supported by a Grants-in-
moderately reducing conditions exhibited bulk
Aid for Scientific Research by
superconductivity in the susceptibility measurement
Education, Science, Sports and Culture of Japan
using a SQUID as shown in Fig. 1.
Ministry of
Very close ZFC
and FC magnetization curves indicate the granular
REFERENCES
nature in the present sample.
1. T. Den and T. Kobayashi, Physica C 196 (1992) 141.
nature,
the
sample
Reflecting this
showed
broad
resistivity
transition with a Te(onset) of 62K as shown in Fig. 2
0.1
•
.
.
,
.
.
,
-
.
,
.
.
.
12
,
FeSr2YCuzOy
FeSr2YCu20z.86 annealed in high P(02)
% i
10
8
0
-0.1 t~
4-; -0.2
-0.3
FC
0
'''
H= 0.5Oe
20
"
. . . . . . . . . . 40 60 80
2
0
0 100
TIK
Fig. 1 ZFCandFCmagnetizationcurvesofFe1212.
0
50
100
150
TIK
Fig. 2 Temperaturedependenceof resistivity for F¢1212.
Physica C 341-348 (2000) 563-564
www.elsevier.nl/Iocate/physc
Discovery of Superconductivity in Fe-Based Cuprates J. Shimoyama, K. Otzschi, T. Hinouchi and K. Kishio Department of Superconductivity, University of Tokyo 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan The Fe-based cuprates, FeSr2YCu2Oy[Fe1212] and relating compounds were found to exhibit superconductivity with Te(onset) up to 62K. Additional annealing process under moderately reducing atmosphere is believed to be crucial for suppression of site exchange between Fe and Cu, resulting in the new superconducting system.
showed discontinuity between y=7.2 and 7.5
1. INTRODUCTION
similarly in the case of SrFeO3.8, while y changed Partial substitution of high-valence metals, such
continuously
in the conventional
phase
with
as Fe, Re, W, ..., for Cu to the so-called chain site,
temperature and P(O2).
Cu(1), has been known to be effective for stabilizing
exchange between Fe and Cu occurred in the
YSr2Cu3Oy phase. In particular, Fe can fully
conventional
substitute Cu(1) site, however, the superconductivity
superconductivity
has been reported only in a narrow compositional
eliminated by annealing under moderately reducing
range of x=0.3~0.4 in
(CUl.xFex)YSr2Cu20y[1].
phase,
This suggested that the site which
of Fe1212,
might
suppress
and it can be
conditions.
Disappearance of superconductivity in higher Fe
In the present study, we have attempted to make
concentration, x>0.5, was believed to be due to the
the Fe1212 compounds to be new superconductors
insufficient hole carrier concentration in the material.
by applying the reducing process prior to the
In our preliminary study on the themogravimetry
oxygenation annealing.
performed for FeSr2YCu2Oy [Fe1212], behaviors of the
oxygen nonstoichiometry in the
Fe1212
2. EXPERIMENTAL
dramatically changed after holding under moderately
Sintered bulk samples of FeSr2YCu2Oy were
reducing conditions, -1073K and P(O2)=102pa.
synthesized by conventional solid state reaction
The new phase was confirmed to maintain the
starting from high purity powders of Fe203, SrCO3,
original Fe1212 structure without significant change
Y203 and CuO. Powder mixture was calcined at
in its lattice constants. Oxygen nonstoichiometry of the new phase
1173K for 12h and sintered at 1223K over 24h in air. The resulting samples were annealed at -1073K
0921-4534/00/$ - see front matter @ 2000 Elsevier Science B.V PII S0921-4534(00)00593-1
All rights reserved.
J. Shimoyama et al./Physica C 341-348 (2000) 563-564
564
under flowing a reducing gas with P(O2) = 102pa for 5h, then cooled down to 573K and changed atmosphere to P(O2)=105Pa.
Finally, high pressure
oxygen annealing, at 523K in P(O2)=3.5 x 107pa for 24h,
was
performed.
Samples
with
compositions of FeSr2(Y,Ca)Cu2Oy
and zero resistance was attained at 25K. Samples of FeSr2(Y0.9Cao.1)Cu2Oy also showed superconductivity, however, Tc was not improved further.
nominal
were also
synthesized in a similar way.
4. CONCLUSIONS The Fe1212 compounds were found to show superconductivity by applying annealing process
3. RESULTS AND DISCUSSIONS
under moderately reducing conditions, which is
The Fe1212 samples prepared without reducing annealing process did not show any sign of
believed to suppress incorporation of Fe to the CuO2-plane in the present system,
superconductivity even after the high pressure oxygen annealing, which increased y to 7.64.
On
the other hand, the samples annealed under
ACKNOWLEDGEMENT This work was partially supported by a Grants-in-
moderately reducing conditions exhibited bulk
Aid for Scientific Research by
superconductivity in the susceptibility measurement
Education, Science, Sports and Culture of Japan
using a SQUID as shown in Fig. 1.
Ministry of
Very close ZFC
and FC magnetization curves indicate the granular
REFERENCES
nature in the present sample.
1. T. Den and T. Kobayashi, Physica C 196 (1992) 141.
nature,
the
sample
Reflecting this
showed
broad
resistivity
transition with a Te(onset) of 62K as shown in Fig. 2
0.1
•
.
.
,
.
.
,
-
.
,
.
.
.
12
,
FeSr2YCuzOy
FeSr2YCu20z.86 annealed in high P(02)
% i
10
8
0
-0.1 t~
4-; -0.2
-0.3
FC
0
'''
H= 0.5Oe
20
"
. . . . . . . . . . 40 60 80
2
0
0 100
TIK
Fig. 1 ZFCandFCmagnetizationcurvesofFe1212.
0
50
100
150
TIK
Fig. 2 Temperaturedependenceof resistivity for F¢1212.