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Superconducting properties of Bi2(LaxLn1−x)yCa3−yCu2Oz (Ln=Y, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Tm)
PhysicaC 165 (1990) 143-146 North-Holland
SUPERCONDUCTING PROPERTIES Gd, Tb, Dy, Ho, Er AND Tm) Takashi KAWANO, Fumio MUNAKATA, and Shoji TANAKA
OF Bil(La,Lnl_,),,Ca3_,Cu20Z
Takaaki IKEMACHI,
(Ln=Y,
Ce, Pr, Nd, Sm, Eu,
Ayumi NOZAKI,
H. YAMAUCHI
*
Superconductivity Research Laboratory, International Superconductivity Technology Center, IO-13 Shinonome I-Chome, KotoKu, Tokyo, 135, Japan
Received 9 November 1989
Oxide superconductors, Bi2(LaxLnl_,)Fag--yCu20r (Ln=Y or rare-earth element), have been synthesized by doping an additional rare-earth element in the Bi-La-Ca-Cu-0 compounds. The zero resistivity superconducting transition temperature of the sample with x=0.5 and y=O.5 increased by about 20 K to be 45 K when compared with the Bi-Ln-Ca-Cu-0 (Ln=La, Nd and Pr) superconductors.
A new family of &-free Bi cuprate superconductors was found by Inoue et al. [ 11 in the Bi-La-CaCu-0 system. Recently, we reported [2] that Bi,Ln,Ca,_,Cu,O, (Ln=Pr and Nd) were also superconductors. The crystal structures of these Sr-free Bi cuprates were found to be similar to that of Bi,Sr$aCu,O, which had a T, of about 80 K. The superconducting onset temperatures ( TF’ ) and the zero resistance temperatures ( Tyd ) of the Sr-free Bi were much lower than those of cuprates BizSr,CaCuzO,. For example, TF’=50 K and TFd = 24 K were obtained for Bi,Nd0.3Ca2,,Cu20, Since the spans between Tp%’ and TTd of these Srfree Bi cuprate superconductors were wide, it was expected that similar compounds might have TEnd’s higher than 24 K. In this paper, we report on the syntheses of Biz (La,Ln, _-x)yCa3_-yCu20r (Ln = Y and rare-earth elements excluding La, Yb and Lu) by doping a rareearth element to the Bi-La-Ca-Cu-0 compounds. It will be demonstrated that some of these Bi-La-LnCa-Cu-0 compounds have TEnd’s nearly twice as high as that of Bi2Nd,,&a2.,Cu20y Samples of Biz(LaxLnl-x),Ca3-yCu~O~ (0.2~~~0.8, 0.31~10.8) were synthesized by a l
Leave of absence from The Faculty of Engineering, The University of Windsor, Windsor, Ontario N9B 3P4, Canada.
0921-4534/90/$03.50 0 Elsevier Science Publishers B.V. (North-Holland )
solid state reaction with BiZOs, CaC03, CuO and Lnz03 (Ln = Y or one of the rare-earth elements excluding Ce, Pr and Tb), CeO,, Pr,O,, or Tb407 powders of purity higher than 99.9% as starting materials. The powders were mixed to an appropriate ratio and the mixed powder was pressed into pellets and calcined at 800” C for 10 h in air. The pellets were reground and pressed into parallelepiped bars of 3 x 3 x 20 mm3. The bars were sintered at 840°C for 35 h in 99.99% pure O2 gas flow and cooled to 500°C at a rate of 60’ C/h. Then the samples were annealed at 500°C for 10 h in O2 gas flow and cooled to room temperature at the same rate. The electrical resistivity of the samples was measured by a standard fourprobe method. DC magnetization was also measured by using a SQUID magnetometer (QUANTUM DESIGN: Mode1 MPM). The crystal structures of the samples were analyzed by powder X-ray diffraction using CuKa! radiation at room temperature over a 2 13range from 3’ to 65 ‘. In table I, Tc’s measured are listed in terms of the doping element, Ln, in Bi2( LaLn),&a2.5CuZOz (Ln= y and rare-earth elements excluding La). The superconducting onset temperatures of the samples except those with Ln=Yb and Lu were located in a range of 50 K to 72 K, and the sample with Ln=Pr had the highest Tznd of 45 K. On the other hand, both samples with Ln=Yb and Lu showed semiconduc-
T. Kawano et al. /Superconducting
144
propertiesoj‘Bi-La-Ln-Ca-C’u-0
Table I Superconducting transition temperatures ( Tyse’ and Tyd ) of Bi,( LaLn),,Ca,,CuZO, with Ln = Yb and Lu were non-superconductive Ln
Tp=’
Y Ce Pr Nd Sm Eu Gd
60 58 68 70 60 68 67
(K)
Ln=
.2201
Ty“ (K)
Ln
Tp,,,
29 4.2 45 40 34 30 35
Tb Dy Ho Er Tm Yb Lu
72 67 57 50 50 -
Pr
phase
I ~ i’,
Ln=Yb
I l
1I
.ll
I. X-ray diffraction
phase
I
2 8 Fig.
.2 201
I
patterns
determmed
(K)
ryd
from electrical
reststivity.
Samples
(K)
30 I2 25 16 4.2 _ _
Since the sample with Ln=Pr had the highest 7’znd among those of Biz( LaLn)o,sCa,,,CuZO,, it is worthwhile to investigate the superconducting temperature of Bi2( La,Pr, _ ,) ,Ca,_,CuzO, in terms of s (the ratio La/Pr) and .r (the total amount of the dopants La and Pr). First. the effect of .Y was examined when the total amount of La and Pr was fixed at y=O.5. Fig. 2 shows the temperature dependence of the resistivity of Biz( La,Pr,_,)o.sCaz.sCuzO= for 0.2~~~0.8. The superconductivity onset temperatures are in the range of 60 K to 70 K. The zero resistance temperatures are observed for the samples with .w=O.2, 0.4 and 0.8 at 42 K and for those with x-=0.5 and 0.6 at 45 K. That is, those samples with the La/Pr ratio near 1/I exhibited the highest TEnd. Secondly, the effect of the total amount of La and Pr, i.e. JJ, was examined fixing the ratio of La/ Pr at l/ 1. Fig. 3 shows the temperature dependence
(degrees) for Bi2Lao.z5Ln0.Z5Ca2 &u20,.
tive behavior. Fig. 1 shows the powder X-ray diffraction pattern for the samples with Ln = Pr and Yb. The diffraction pattern of the superconducting sample with Ln=Pr is nearly identical to that of Bi,Sr,CaCuzO,, (the 22 12 phase) but contains small peaks due to a.secondary phase which is likely to be Bi,Sr,CuO, (the 2201 phase). Contrary to these samples, the non-superconducting sample with Ln = Yb mainly consists of a phase of the 220 1 type. The reason why the sample with Ln=Yb does not contain a phase of the 22 12 type may be that the radius of a Yb ion is significantly smaller than those of the other rare-earth elements (except Lu).
4i
Temperature
(K)
Fig. 2. Temperature dependence of electrical resistrvity Bi,( La,Pr, _\),, sCaz.sCuzO, for different x values.
of
T. Kawano et al. /Superconducting
50
100
Temperature Fig. 3. Temperature Biz( LaPr),Caz.,CuzO,
E
'0 .z z $j rn
dependence for different
(K)
of electrical y values.
resistivity
of
-3 -4 -5
cooling
-6
20
40
in a
field of 5 Oe'
60
60
100
Temperature(K)
Fig. 4. Temperature Bi,(LaPr),.,Ca,,CurO,.
dependence
of DC
magnetization
properties ofBi-La-Ln-Ca-Cu-0
145
elled off at 20 K. The volume fraction was about 40% of a full Meissner effect at 5 K. The composition of this compound was analyzed by EDX (Kevex:Delta Analyzer) Class and found to be Bi,.8Lao.zPro.2Ca2,SCu20ywhich was very close to the nominal composition. In fig. 5, T, of Biz(LaLn)0.5Ca2.SCuZOz is plotted against the mean ionic radius for La and Ln (open circles), and also T, of Biz(La,Pr,_x)0.5Ca2.5CuZOz against the mean ionic radius for La and Pr (solid triangles). For the ionic radii of Ln’s, the values given by R.D. Shannon were employed [ 31. T, increases monotonically as the mean ionic radius increases. When the mean ionic radius reaches a value around 1.14 A, T, gets levelled off. If the data by Inoue et al. [ 1 ] is taken into account, T, may be lowered when the mean ionic radius increases beyond 1.14 A. The following two reasons may be thought for the T, change with respect to the mean ionic radius of the two rare-earth elements. (I ) Assuming that the valence numbers of Ln’s excluding Ce are all 3+ and all the samples have the same oxygen content, the difference in the crystal structure including the difference in the lattice parameters or in the modulated structure, may affect the superconducting transition temperature. For example, the lattice parameters of Ln=Pr, Gd and Er were: a=5.40 A and c=29.95 A for Ln=Pr, az5.40 A and c=29.89 A for Ln=Gd, and a=5.39 A and ~~29.88 A for Ln=Er. The lattice parameters were slightly different. The differ-
of
of the resistivity of Biz(LaPr),Ca,_,CuzO, for 0.3SySO.8. For the samples with y=O.3-0.6, the zero resistivity temperatures were in the range of 3 1 K to 45 K. For the sample with y=O.7, the resistivity started to decrease at 62 K, but zero resistivity did not show above 4.2 K. The sample with y=O.8 showed semiconductive behavior. The sample with y=O.5 had the highest Tyd of 45 K. The La/Pr ratio little afffected the value of T,. On the contrary the total amount of La and Pr significantly affected the value of T,. Fig. 4 shows the DC magnetization of Biz(LaPr)o.sCa2.5Cu20, which has the highest TEnd of 45 K. The magnetic superconducting onset temperature was 62 K. The superconducting volume fraction gradually increased below 62 K and got lev-
Ionic
Radius
( A )
Fig. 5. Superconducting transition temperature T, as a function ofthe mean ionic radius for La and Ln in Bi2(LaLn)0.5Ca2.5CuZOZ (open circles) and the mean ionic radius for La and Pr in Biz( LaxPr, _,)o.sCaz.sCulO, (solid triangles).
146
T. Kawano et al. /Superconducting
ence in the length of the lattice parameters may be due to the difference in the oxygen concentration. Unfortunately the oxygen concentration was not able to be determined because all of the samples were not single phase. (2) Also assuming that the valence numbers of Ln’s excluding Ce are all 3-t and oxygen contents of the samples are now different, the hole concentration controlled by the oxygen content may have an influence on the superconducting transition temperature. It was pointed out that different hole concentrations gave rise to different superconducting transition temperatures in BizSr&aCuzO, [ 4.5 1. At present, we have no definite experimental data to eliminate any of of these cases. Further investigations in the crystal structure and the oxygen content are in progress. In oxide superconductors. summary, Bi,(La,Ln,__,).Ca,_,.Cu,O, (Ln=Y or a rare-earth element ), have been synthesized by adding on rareearth elements to the Bi-La-Ca-Cu-0 compounds. The highest superconducting transition temperature ( TEnd) was obtained for the sample with x=0.5 and
properties
qfBi-La-Ln-Ca-C&O
v=O.5 at 45 K. This value was about 20 K higher than TFd’s measured for the Bi-Ln-Ca-Cu-0 (Ln = La, Nd and Pr) superconductors.
Acknowledgement
We would like to thank T. Kaneko for his help in the magnetization measurement.
References [I ] 0. Inoue, S. Adachi. Y. Takahashi. H. Hirano and S. Kawashima, Jpn. J. Appl. Phys. 28 (1989) L778. [2] T. Kawano, F. Munakata, A. Nozaki. T. Ikemachi. H. Yamauchi and S. Tanaka, Physica C. to be submitted. [ 31 R.D. Shannon, Acta Crystallog. A32 ( 1976) L75 I. [4] B. Jayaram, P.C. Lanchester and M.T. Weller. Physica C 160 (1989) L17. [5] Y. Koike, Y. Iwabuchi, S. Hosoya, N. Kobayashi and T. Fukase. Physica C 159 (1989) L105.
SUPERCONDUCTING PROPERTIES Gd, Tb, Dy, Ho, Er AND Tm) Takashi KAWANO, Fumio MUNAKATA, and Shoji TANAKA
OF Bil(La,Lnl_,),,Ca3_,Cu20Z
Takaaki IKEMACHI,
(Ln=Y,
Ce, Pr, Nd, Sm, Eu,
Ayumi NOZAKI,
H. YAMAUCHI
*
Superconductivity Research Laboratory, International Superconductivity Technology Center, IO-13 Shinonome I-Chome, KotoKu, Tokyo, 135, Japan
Received 9 November 1989
Oxide superconductors, Bi2(LaxLnl_,)Fag--yCu20r (Ln=Y or rare-earth element), have been synthesized by doping an additional rare-earth element in the Bi-La-Ca-Cu-0 compounds. The zero resistivity superconducting transition temperature of the sample with x=0.5 and y=O.5 increased by about 20 K to be 45 K when compared with the Bi-Ln-Ca-Cu-0 (Ln=La, Nd and Pr) superconductors.
A new family of &-free Bi cuprate superconductors was found by Inoue et al. [ 11 in the Bi-La-CaCu-0 system. Recently, we reported [2] that Bi,Ln,Ca,_,Cu,O, (Ln=Pr and Nd) were also superconductors. The crystal structures of these Sr-free Bi cuprates were found to be similar to that of Bi,Sr$aCu,O, which had a T, of about 80 K. The superconducting onset temperatures ( TF’ ) and the zero resistance temperatures ( Tyd ) of the Sr-free Bi were much lower than those of cuprates BizSr,CaCuzO,. For example, TF’=50 K and TFd = 24 K were obtained for Bi,Nd0.3Ca2,,Cu20, Since the spans between Tp%’ and TTd of these Srfree Bi cuprate superconductors were wide, it was expected that similar compounds might have TEnd’s higher than 24 K. In this paper, we report on the syntheses of Biz (La,Ln, _-x)yCa3_-yCu20r (Ln = Y and rare-earth elements excluding La, Yb and Lu) by doping a rareearth element to the Bi-La-Ca-Cu-0 compounds. It will be demonstrated that some of these Bi-La-LnCa-Cu-0 compounds have TEnd’s nearly twice as high as that of Bi2Nd,,&a2.,Cu20y Samples of Biz(LaxLnl-x),Ca3-yCu~O~ (0.2~~~0.8, 0.31~10.8) were synthesized by a l
Leave of absence from The Faculty of Engineering, The University of Windsor, Windsor, Ontario N9B 3P4, Canada.
0921-4534/90/$03.50 0 Elsevier Science Publishers B.V. (North-Holland )
solid state reaction with BiZOs, CaC03, CuO and Lnz03 (Ln = Y or one of the rare-earth elements excluding Ce, Pr and Tb), CeO,, Pr,O,, or Tb407 powders of purity higher than 99.9% as starting materials. The powders were mixed to an appropriate ratio and the mixed powder was pressed into pellets and calcined at 800” C for 10 h in air. The pellets were reground and pressed into parallelepiped bars of 3 x 3 x 20 mm3. The bars were sintered at 840°C for 35 h in 99.99% pure O2 gas flow and cooled to 500°C at a rate of 60’ C/h. Then the samples were annealed at 500°C for 10 h in O2 gas flow and cooled to room temperature at the same rate. The electrical resistivity of the samples was measured by a standard fourprobe method. DC magnetization was also measured by using a SQUID magnetometer (QUANTUM DESIGN: Mode1 MPM). The crystal structures of the samples were analyzed by powder X-ray diffraction using CuKa! radiation at room temperature over a 2 13range from 3’ to 65 ‘. In table I, Tc’s measured are listed in terms of the doping element, Ln, in Bi2( LaLn),&a2.5CuZOz (Ln= y and rare-earth elements excluding La). The superconducting onset temperatures of the samples except those with Ln=Yb and Lu were located in a range of 50 K to 72 K, and the sample with Ln=Pr had the highest Tznd of 45 K. On the other hand, both samples with Ln=Yb and Lu showed semiconduc-
T. Kawano et al. /Superconducting
144
propertiesoj‘Bi-La-Ln-Ca-C’u-0
Table I Superconducting transition temperatures ( Tyse’ and Tyd ) of Bi,( LaLn),,Ca,,CuZO, with Ln = Yb and Lu were non-superconductive Ln
Tp=’
Y Ce Pr Nd Sm Eu Gd
60 58 68 70 60 68 67
(K)
Ln=
.2201
Ty“ (K)
Ln
Tp,,,
29 4.2 45 40 34 30 35
Tb Dy Ho Er Tm Yb Lu
72 67 57 50 50 -
Pr
phase
I ~ i’,
Ln=Yb
I l
1I
.ll
I. X-ray diffraction
phase
I
2 8 Fig.
.2 201
I
patterns
determmed
(K)
ryd
from electrical
reststivity.
Samples
(K)
30 I2 25 16 4.2 _ _
Since the sample with Ln=Pr had the highest 7’znd among those of Biz( LaLn)o,sCa,,,CuZO,, it is worthwhile to investigate the superconducting temperature of Bi2( La,Pr, _ ,) ,Ca,_,CuzO, in terms of s (the ratio La/Pr) and .r (the total amount of the dopants La and Pr). First. the effect of .Y was examined when the total amount of La and Pr was fixed at y=O.5. Fig. 2 shows the temperature dependence of the resistivity of Biz( La,Pr,_,)o.sCaz.sCuzO= for 0.2~~~0.8. The superconductivity onset temperatures are in the range of 60 K to 70 K. The zero resistance temperatures are observed for the samples with .w=O.2, 0.4 and 0.8 at 42 K and for those with x-=0.5 and 0.6 at 45 K. That is, those samples with the La/Pr ratio near 1/I exhibited the highest TEnd. Secondly, the effect of the total amount of La and Pr, i.e. JJ, was examined fixing the ratio of La/ Pr at l/ 1. Fig. 3 shows the temperature dependence
(degrees) for Bi2Lao.z5Ln0.Z5Ca2 &u20,.
tive behavior. Fig. 1 shows the powder X-ray diffraction pattern for the samples with Ln = Pr and Yb. The diffraction pattern of the superconducting sample with Ln=Pr is nearly identical to that of Bi,Sr,CaCuzO,, (the 22 12 phase) but contains small peaks due to a.secondary phase which is likely to be Bi,Sr,CuO, (the 2201 phase). Contrary to these samples, the non-superconducting sample with Ln = Yb mainly consists of a phase of the 220 1 type. The reason why the sample with Ln=Yb does not contain a phase of the 22 12 type may be that the radius of a Yb ion is significantly smaller than those of the other rare-earth elements (except Lu).
4i
Temperature
(K)
Fig. 2. Temperature dependence of electrical resistrvity Bi,( La,Pr, _\),, sCaz.sCuzO, for different x values.
of
T. Kawano et al. /Superconducting
50
100
Temperature Fig. 3. Temperature Biz( LaPr),Caz.,CuzO,
E
'0 .z z $j rn
dependence for different
(K)
of electrical y values.
resistivity
of
-3 -4 -5
cooling
-6
20
40
in a
field of 5 Oe'
60
60
100
Temperature(K)
Fig. 4. Temperature Bi,(LaPr),.,Ca,,CurO,.
dependence
of DC
magnetization
properties ofBi-La-Ln-Ca-Cu-0
145
elled off at 20 K. The volume fraction was about 40% of a full Meissner effect at 5 K. The composition of this compound was analyzed by EDX (Kevex:Delta Analyzer) Class and found to be Bi,.8Lao.zPro.2Ca2,SCu20ywhich was very close to the nominal composition. In fig. 5, T, of Biz(LaLn)0.5Ca2.SCuZOz is plotted against the mean ionic radius for La and Ln (open circles), and also T, of Biz(La,Pr,_x)0.5Ca2.5CuZOz against the mean ionic radius for La and Pr (solid triangles). For the ionic radii of Ln’s, the values given by R.D. Shannon were employed [ 31. T, increases monotonically as the mean ionic radius increases. When the mean ionic radius reaches a value around 1.14 A, T, gets levelled off. If the data by Inoue et al. [ 1 ] is taken into account, T, may be lowered when the mean ionic radius increases beyond 1.14 A. The following two reasons may be thought for the T, change with respect to the mean ionic radius of the two rare-earth elements. (I ) Assuming that the valence numbers of Ln’s excluding Ce are all 3+ and all the samples have the same oxygen content, the difference in the crystal structure including the difference in the lattice parameters or in the modulated structure, may affect the superconducting transition temperature. For example, the lattice parameters of Ln=Pr, Gd and Er were: a=5.40 A and c=29.95 A for Ln=Pr, az5.40 A and c=29.89 A for Ln=Gd, and a=5.39 A and ~~29.88 A for Ln=Er. The lattice parameters were slightly different. The differ-
of
of the resistivity of Biz(LaPr),Ca,_,CuzO, for 0.3SySO.8. For the samples with y=O.3-0.6, the zero resistivity temperatures were in the range of 3 1 K to 45 K. For the sample with y=O.7, the resistivity started to decrease at 62 K, but zero resistivity did not show above 4.2 K. The sample with y=O.8 showed semiconductive behavior. The sample with y=O.5 had the highest Tyd of 45 K. The La/Pr ratio little afffected the value of T,. On the contrary the total amount of La and Pr significantly affected the value of T,. Fig. 4 shows the DC magnetization of Biz(LaPr)o.sCa2.5Cu20, which has the highest TEnd of 45 K. The magnetic superconducting onset temperature was 62 K. The superconducting volume fraction gradually increased below 62 K and got lev-
Ionic
Radius
( A )
Fig. 5. Superconducting transition temperature T, as a function ofthe mean ionic radius for La and Ln in Bi2(LaLn)0.5Ca2.5CuZOZ (open circles) and the mean ionic radius for La and Pr in Biz( LaxPr, _,)o.sCaz.sCulO, (solid triangles).
146
T. Kawano et al. /Superconducting
ence in the length of the lattice parameters may be due to the difference in the oxygen concentration. Unfortunately the oxygen concentration was not able to be determined because all of the samples were not single phase. (2) Also assuming that the valence numbers of Ln’s excluding Ce are all 3-t and oxygen contents of the samples are now different, the hole concentration controlled by the oxygen content may have an influence on the superconducting transition temperature. It was pointed out that different hole concentrations gave rise to different superconducting transition temperatures in BizSr&aCuzO, [ 4.5 1. At present, we have no definite experimental data to eliminate any of of these cases. Further investigations in the crystal structure and the oxygen content are in progress. In oxide superconductors. summary, Bi,(La,Ln,__,).Ca,_,.Cu,O, (Ln=Y or a rare-earth element ), have been synthesized by adding on rareearth elements to the Bi-La-Ca-Cu-0 compounds. The highest superconducting transition temperature ( TEnd) was obtained for the sample with x=0.5 and
properties
qfBi-La-Ln-Ca-C&O
v=O.5 at 45 K. This value was about 20 K higher than TFd’s measured for the Bi-Ln-Ca-Cu-0 (Ln = La, Nd and Pr) superconductors.
Acknowledgement
We would like to thank T. Kaneko for his help in the magnetization measurement.
References [I ] 0. Inoue, S. Adachi. Y. Takahashi. H. Hirano and S. Kawashima, Jpn. J. Appl. Phys. 28 (1989) L778. [2] T. Kawano, F. Munakata, A. Nozaki. T. Ikemachi. H. Yamauchi and S. Tanaka, Physica C. to be submitted. [ 31 R.D. Shannon, Acta Crystallog. A32 ( 1976) L75 I. [4] B. Jayaram, P.C. Lanchester and M.T. Weller. Physica C 160 (1989) L17. [5] Y. Koike, Y. Iwabuchi, S. Hosoya, N. Kobayashi and T. Fukase. Physica C 159 (1989) L105.