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Synthesis of a new series of 1222 Pb-based cuprates, (Pb,Cd)(Sr,R)2(R′,Ce)2Cu2O2 (R, R′ = rare-earth elements)
ELSEVIER
Jownal
of
Alloys and Compounds 24s
Ruccivcd
(lW3) 20-22
.31 Mw_ IYYh
Abstract
(Pb.Cd)-I222 compounds with nominal compositions of (Ph,,
merits. R and R’. in (Pb.Cd)(Sr.R),(R’,Ce)2CU20,.
1. Introduction
We have known since a nonsuperconductor (Pb.Cu)(Sr.Pr),Pr,Cu,O~ was synthesized by Adachi et al. [I] that this phase is isomorphous to TISrZ(Nd.Ce),Cu,O, [2]. That is the (Pb,Cu)-‘1222’ structure contains (Ph.Cu)O monolayers instead of the TlO monolayers of the Tl-‘1222’structure. After that. (Pb.Cu)(Sr,Eu),( Eu.Cc),Cu,O, as a new superconducting compound having ‘fluorite-type’ block kyers was discovered by Maeda et al. (31. Subsequently, careful
research
was
carried
out
on
the
system
(Pb,Cu)( Sr.R)-,( R’,Ce)Cu,O: (R. R’ = rare-earth elements), and a series of single-phase and superconducting (Pb,Cu)-1222 compounds were obtained [3-61. Considering that Cd behaves similarly to Cu, and can partially replace Pb in the Pb-based compounds [7,8], we suggested that the (Pb,Cd)-1222 phase should also be formed. In this paper, a new series of single or nearly single-phase (Pb,Cd)-1222 compounds were obtained using a single or a pair of rare-earth ele-
-*Correspondingauthor. oY2S-83iW%/$15.00
PII
0 FM Elsevier Science BY, Ail rights reserved SOY25-838H( 96302487-S
the
composition
of
2. Experimental details The sampies were prepared by the conventional solid-state reaction method using high purity powders of oxides and carbonates of the metallic elements. The powders were mixed so as to yield the nominal composition (Pb,,,sCd,,.s)(Sr,,.,R,,., )2(R’,,,,Ce,,.~),Cu,0;, R = R’= Y, La, Nd, Pr, Sm. Eu, Gd, Dy, Ho, Er,
Tm and (R. R’) = (La, Eu), (Sm, Gd), (Sm. Eu), (La, Gd), (Eu, Gd), (Nd, Eu), (Nd, Dy), (Nd,Y), (Nd, Er). The stoichiometrically mlved powders were well ground in an agate mortar and preheated at 830°C in air for 20 h. Then the samples were re-ground and pressed inlo pellels, calcined in air at 1030 “C for 7 h and then furnace-cooled to room temperature. The
X-ray diffraction (XRD) patterns were taken with a Japan Rigaku Dmax-r, diffractometer with silicon powder as internal standard. Cu Kar radiation was used. Selected area electron diffraction (WED) patterns were recorded in a Hitachi model H-800 transmission electron microscope. The resistivities of the
Fis.
2.
((id
.(‘c.
The
(PIT,,
for (h) loo.
SAED patterns
I <‘u c) : (a) ml:
the rcactitrn time was rcductzd to 2.5-3 h. the sample
(K.
contained (Pb.Cd)-1222 phase as of the (Pb.Cd)-1212 type and C’&.. (marked with asterisks and dots rcspcctivcl!: in Fig. I ). The rare-earth elements such as
\vith
R’)
= (Y.
U)
the main phase and impurities
Pr.Sm.Eu.Gd.Dy, Y and Ho
10
20
30
so
40
60
were rather favorable
70
28 (dg)
?? SO 0
samples wcrc measurccl hy the standard four-probe method with indium contacts. down to 15 K.
R’,Cc
0
0
0
Pb,Cd
??
CU
3. Results and discussion Among the samples in which R = R’. XRD patterns revealed that the samples with Y, Pr. Sm, Eu. Gd. Dy. or Ho were single or nearly single-phase [Y.lO]. When
Tablut La.Eu (1
(A)
c (A) rcs, HI (A) r,,,,,, (A) v (A’)
3.841 29.30 1.135 4$:w)Z
.z.
Nd.EU 3.835 2Y.2 1
Sm.Eu 3.x3.5 ‘Y.31
LACki 3.x3
Eldill
I
29.3 I
3.x30 29.31)
Nd,Dy
3.m _ ‘4 ._ ‘7
3.824 29.29
I.131
I.13
1.128
I.!3
I.128
I.131
I.(H)2
I in)?
o.ws
0.945
11.W
o.%o
429.6
431.3
430.X
-PM
-12x.5
m.3
Nd.Er
?I.813 _ ‘9 ._ ‘6, 1.131 0.039 5x4
Nd.Y 3.817 29.18
Y-Y 3.8!4 29.18
1.131
1.m
o.Y&
0.946
-a.1
424.5
FIN. -1. ‘i‘~mpsraturu
dcpcnduncu of clcclricd
(Sm. ELI). (ELI. Cid).
rcsistivity for sampIts with (R. R’) = (Sm. Gd).
for R = R’ in the formation of the (Pb.Cd)-1222 phase as well as the (Pb.Cu)-1222 phase. Among the samples with a pair of rare-earth elements. the samples with (R. R’) = (La. Eu). (Sm. Cd). (Sm. Eu). (La, Gd), (Eu. Gd). (Nd. Eu). (Nd. Dy). (Nd. Er). (Nd.Y) were practically pure or nearly pure phase. The XRD patterns are shown in Fig. 1. It was shown that the comparatively small ions in the fluorite block arc unfavorable to the formation of (Pb,Cd)-1222 phase. such as (R. R’)=(Y. Y). (Nd. Y) and (Nd. Er) (see Fig. I). Most of the diffraction lines for the invcstigated samples could be indexed for the body-centered tetragonal unit cell: the lattice parameters are listed in Table 1. We can see that the cell volumes were approximately proportional to the effective ionic raaius of (Sr.R) and (R’,Ce) sites. The SAED patterns also confirmed the formation of the (Pb,Cd)-1222 compounds. and no superlattice reflections could be detected. The lattice parameters obtained from the SAED patterns for (R, R’) = (Sm. Gd) sample (Fig. 2) are ;1= 3.826 k and c = 29.27 A, and are consistent with the XRD measurements. Fig. 1 shows that the XRD patterns for the (Ph.Cd)-1222 phase are similar to those of the (Pb,Cu)-1222 phase f3-61. This result suggests that the (PI-&d)-1222 compound has a crystal structure similar to that of the (Pb.Cu)-1222 compound. Fig. 3 schematically shows the ideal crystal structure of (Ph,Cd)( Sr,R)2( R’,Ce)+tzO,. The refined atomic positions for the sample with R = R’= Ho have been reported in a previous paper [9]. We found that the atomic positions of (Pb,Cd) and the 0 atoms in the (Pb,Cd)O monolayer of the (Pb,Cd)-1222 compound were displaced from their ideal positions, as previously reported for the (Pb,Cu)-1212 or (Pb,Cu)-1222 compounds. (Pb,, sCuo.s)(Sro.&,., )#G.,Ce,r..l ),Cu,O, samples with (R, R’) = (Sm, Eu), (Nd, Eu), (La, Eu), (Eu, Gd)
superconducting [4]. But resistivity measurements (Fig. 4) showed that all these (Pb.Cd)-1222 compounds were narrow gap semiconductors under present preparation conditions. It is possible that upon adjusting the firing temperature or by post-annealing under high oxygen pressure, such compounds might become superconductors. Further work on trying lo obtain superconductivity is in progress.
were
4.
Conclusions
A series of new (Pb.Cd)-1222 compounds (Pb,Cd)(Sr,R),( R:Ce),Cu,O, have been prepared successfully and characterized. All the compounds are isostructural with the (Pb,Cu)-I222 phase.
References 1II S. Adachi. 0. Inonc. S. Kawashima. Sctsunc and K. Wasa, Pt~picu 12) C. Martin.
D. Buurgaull.
EL Raveau. Mod. Phys.
C.
H. Adachi. Y. Ichikawa. 168 (1yW)
M. Hcrvicu, Lrtt.
C. Michel. J. Provosl and
B, _? (WY)
993.
S. Koriyanra. A. lchlinosc. Yamauchi and S. Tanaka, Physiccr C, IhY ( IWl) 13.7.
[3\ T.
Macda.
K.
Sakuyama,
141 T. Macda. K. Sakuyama. N. Sakai. H. Yamauchi Physica
c.
177
[6]
H.
and S. Tanaka.
( I’)91) 33.
[S] T. Macda. N. Sakai. F. Izumi. T. Wada. H. Yamauchi. Physka
and S. Tanaka,
K.
1.
N. Sakai. T. Macda.
C,
lY.3 (1992)
H. Yamauchi
H. Asano
73.
and S. Tanaka.
Physica
C.
212 (1993) 7s. [71 T.l? Beaks.
rison, D.M. T&no/..
C. Dineen, W.G. Jacobson and
5 ( 1992)
Freeman,
S.R. Hall,
S.J. Zammattio.
M.R.
Supercunrl.
HarSci.
47.
[8] J.M. Min, J.K. Liang, X.L. Chen. C. Wang, C. Dong end G.H. Rao, Physb [9] H.M.
C. 229 ( 1994)
Luo. Z.X.
Zhao.
G.C.
169. Che. F. Wu. H. Chen. C. Dong.
Z.Y. Chen and Y.T. Qian. 1. Solid
[IO]J.R. Min, /%.D. Thesis. Bcjing.199~5%.
Stare Chem.,
123
(19%)313.
Institute of Physics, Academia Sinica,
Jownal
of
Alloys and Compounds 24s
Ruccivcd
(lW3) 20-22
.31 Mw_ IYYh
Abstract
(Pb.Cd)-I222 compounds with nominal compositions of (Ph,,
merits. R and R’. in (Pb.Cd)(Sr.R),(R’,Ce)2CU20,.
1. Introduction
We have known since a nonsuperconductor (Pb.Cu)(Sr.Pr),Pr,Cu,O~ was synthesized by Adachi et al. [I] that this phase is isomorphous to TISrZ(Nd.Ce),Cu,O, [2]. That is the (Pb,Cu)-‘1222’ structure contains (Ph.Cu)O monolayers instead of the TlO monolayers of the Tl-‘1222’structure. After that. (Pb.Cu)(Sr,Eu),( Eu.Cc),Cu,O, as a new superconducting compound having ‘fluorite-type’ block kyers was discovered by Maeda et al. (31. Subsequently, careful
research
was
carried
out
on
the
system
(Pb,Cu)( Sr.R)-,( R’,Ce)Cu,O: (R. R’ = rare-earth elements), and a series of single-phase and superconducting (Pb,Cu)-1222 compounds were obtained [3-61. Considering that Cd behaves similarly to Cu, and can partially replace Pb in the Pb-based compounds [7,8], we suggested that the (Pb,Cd)-1222 phase should also be formed. In this paper, a new series of single or nearly single-phase (Pb,Cd)-1222 compounds were obtained using a single or a pair of rare-earth ele-
-*Correspondingauthor. oY2S-83iW%/$15.00
PII
0 FM Elsevier Science BY, Ail rights reserved SOY25-838H( 96302487-S
the
composition
of
2. Experimental details The sampies were prepared by the conventional solid-state reaction method using high purity powders of oxides and carbonates of the metallic elements. The powders were mixed so as to yield the nominal composition (Pb,,,sCd,,.s)(Sr,,.,R,,., )2(R’,,,,Ce,,.~),Cu,0;, R = R’= Y, La, Nd, Pr, Sm. Eu, Gd, Dy, Ho, Er,
Tm and (R. R’) = (La, Eu), (Sm, Gd), (Sm. Eu), (La, Gd), (Eu, Gd), (Nd, Eu), (Nd, Dy), (Nd,Y), (Nd, Er). The stoichiometrically mlved powders were well ground in an agate mortar and preheated at 830°C in air for 20 h. Then the samples were re-ground and pressed inlo pellels, calcined in air at 1030 “C for 7 h and then furnace-cooled to room temperature. The
X-ray diffraction (XRD) patterns were taken with a Japan Rigaku Dmax-r, diffractometer with silicon powder as internal standard. Cu Kar radiation was used. Selected area electron diffraction (WED) patterns were recorded in a Hitachi model H-800 transmission electron microscope. The resistivities of the
Fis.
2.
((id
.(‘c.
The
(PIT,,
for (h) loo.
SAED patterns
I <‘u c) : (a) ml:
the rcactitrn time was rcductzd to 2.5-3 h. the sample
(K.
contained (Pb.Cd)-1222 phase as of the (Pb.Cd)-1212 type and C’&.. (marked with asterisks and dots rcspcctivcl!: in Fig. I ). The rare-earth elements such as
\vith
R’)
= (Y.
U)
the main phase and impurities
Pr.Sm.Eu.Gd.Dy, Y and Ho
10
20
30
so
40
60
were rather favorable
70
28 (dg)
?? SO 0
samples wcrc measurccl hy the standard four-probe method with indium contacts. down to 15 K.
R’,Cc
0
0
0
Pb,Cd
??
CU
3. Results and discussion Among the samples in which R = R’. XRD patterns revealed that the samples with Y, Pr. Sm, Eu. Gd. Dy. or Ho were single or nearly single-phase [Y.lO]. When
Tablut La.Eu (1
(A)
c (A) rcs, HI (A) r,,,,,, (A) v (A’)
3.841 29.30 1.135 4$:w)Z
.z.
Nd.EU 3.835 2Y.2 1
Sm.Eu 3.x3.5 ‘Y.31
LACki 3.x3
Eldill
I
29.3 I
3.x30 29.31)
Nd,Dy
3.m _ ‘4 ._ ‘7
3.824 29.29
I.131
I.13
1.128
I.!3
I.128
I.131
I.(H)2
I in)?
o.ws
0.945
11.W
o.%o
429.6
431.3
430.X
-PM
-12x.5
m.3
Nd.Er
?I.813 _ ‘9 ._ ‘6, 1.131 0.039 5x4
Nd.Y 3.817 29.18
Y-Y 3.8!4 29.18
1.131
1.m
o.Y&
0.946
-a.1
424.5
FIN. -1. ‘i‘~mpsraturu
dcpcnduncu of clcclricd
(Sm. ELI). (ELI. Cid).
rcsistivity for sampIts with (R. R’) = (Sm. Gd).
for R = R’ in the formation of the (Pb.Cd)-1222 phase as well as the (Pb.Cu)-1222 phase. Among the samples with a pair of rare-earth elements. the samples with (R. R’) = (La. Eu). (Sm. Cd). (Sm. Eu). (La, Gd), (Eu. Gd). (Nd. Eu). (Nd. Dy). (Nd. Er). (Nd.Y) were practically pure or nearly pure phase. The XRD patterns are shown in Fig. 1. It was shown that the comparatively small ions in the fluorite block arc unfavorable to the formation of (Pb,Cd)-1222 phase. such as (R. R’)=(Y. Y). (Nd. Y) and (Nd. Er) (see Fig. I). Most of the diffraction lines for the invcstigated samples could be indexed for the body-centered tetragonal unit cell: the lattice parameters are listed in Table 1. We can see that the cell volumes were approximately proportional to the effective ionic raaius of (Sr.R) and (R’,Ce) sites. The SAED patterns also confirmed the formation of the (Pb,Cd)-1222 compounds. and no superlattice reflections could be detected. The lattice parameters obtained from the SAED patterns for (R, R’) = (Sm. Gd) sample (Fig. 2) are ;1= 3.826 k and c = 29.27 A, and are consistent with the XRD measurements. Fig. 1 shows that the XRD patterns for the (Ph.Cd)-1222 phase are similar to those of the (Pb,Cu)-1222 phase f3-61. This result suggests that the (PI-&d)-1222 compound has a crystal structure similar to that of the (Pb.Cu)-1222 compound. Fig. 3 schematically shows the ideal crystal structure of (Ph,Cd)( Sr,R)2( R’,Ce)+tzO,. The refined atomic positions for the sample with R = R’= Ho have been reported in a previous paper [9]. We found that the atomic positions of (Pb,Cd) and the 0 atoms in the (Pb,Cd)O monolayer of the (Pb,Cd)-1222 compound were displaced from their ideal positions, as previously reported for the (Pb,Cu)-1212 or (Pb,Cu)-1222 compounds. (Pb,, sCuo.s)(Sro.&,., )#G.,Ce,r..l ),Cu,O, samples with (R, R’) = (Sm, Eu), (Nd, Eu), (La, Eu), (Eu, Gd)
superconducting [4]. But resistivity measurements (Fig. 4) showed that all these (Pb.Cd)-1222 compounds were narrow gap semiconductors under present preparation conditions. It is possible that upon adjusting the firing temperature or by post-annealing under high oxygen pressure, such compounds might become superconductors. Further work on trying lo obtain superconductivity is in progress.
were
4.
Conclusions
A series of new (Pb.Cd)-1222 compounds (Pb,Cd)(Sr,R),( R:Ce),Cu,O, have been prepared successfully and characterized. All the compounds are isostructural with the (Pb,Cu)-I222 phase.
References 1II S. Adachi. 0. Inonc. S. Kawashima. Sctsunc and K. Wasa, Pt~picu 12) C. Martin.
D. Buurgaull.
EL Raveau. Mod. Phys.
C.
H. Adachi. Y. Ichikawa. 168 (1yW)
M. Hcrvicu, Lrtt.
C. Michel. J. Provosl and
B, _? (WY)
993.
S. Koriyanra. A. lchlinosc. Yamauchi and S. Tanaka, Physiccr C, IhY ( IWl) 13.7.
[3\ T.
Macda.
K.
Sakuyama,
141 T. Macda. K. Sakuyama. N. Sakai. H. Yamauchi Physica
c.
177
[6]
H.
and S. Tanaka.
( I’)91) 33.
[S] T. Macda. N. Sakai. F. Izumi. T. Wada. H. Yamauchi. Physka
and S. Tanaka,
K.
1.
N. Sakai. T. Macda.
C,
lY.3 (1992)
H. Yamauchi
H. Asano
73.
and S. Tanaka.
Physica
C.
212 (1993) 7s. [71 T.l? Beaks.
rison, D.M. T&no/..
C. Dineen, W.G. Jacobson and
5 ( 1992)
Freeman,
S.R. Hall,
S.J. Zammattio.
M.R.
Supercunrl.
HarSci.
47.
[8] J.M. Min, J.K. Liang, X.L. Chen. C. Wang, C. Dong end G.H. Rao, Physb [9] H.M.
C. 229 ( 1994)
Luo. Z.X.
Zhao.
G.C.
169. Che. F. Wu. H. Chen. C. Dong.
Z.Y. Chen and Y.T. Qian. 1. Solid
[IO]J.R. Min, /%.D. Thesis. Bcjing.199~5%.
Stare Chem.,
123
(19%)313.
Institute of Physics, Academia Sinica,