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Effect of Sb substitution on Tc in Bi-Pb-Sr-Ca-Cu-O systems
Physica C 158 (1989) 97-101 North-Holland, Amsterdam
EFFECT OF Sb S U B S T I T U T I O N O N Tc IN B i - P b - S r - C a - C u - O SYSTEMS S.X. DOU, H.K. LIU, N.X. TAN, Y.J. SHENG and W.K. JONES ~ School of Materials Science and Engineering, University of New South Wales, P.O. Box 1, Kensington, N S W 2033, Australia College of Engineering and Applied Science, The State University o f Florida at Miami, VH134 Miami, FL 33199, USA Received 9 February 1989
The oxidation states and thereby oxygen non-stoichiometry in B i - S r - C a - C u - O systems have been found to be an important factor for superconductivity. Sb has been doped into B i - P b - S r - C a - C u - O and appears to be pentavalent as evidenced by the reduction of unit cell parameters, and the decrease of Cu 3+ concentration. Sb substitution up to 5% Bi and Pb depressed Tc for sample treated in pure oxygen but not under low oxygen pressure. Cu 3+ is not critical to superconductivity in Bi-based materials as it is in YBa2Cu3OT. The Cu-O2 plane based on Cu 2+ is responsible for sustaining the high T¢. No superconducting phases other than (Bi, Pb, Sb)2Sr2CaCu2Ox (2212) and (Bi, Pb, Sb)zSr2Ca2Cu3Ox (2223) were detected contrary to previous report. Sb doping weakens the superlattice considerably due to relief of the strain in Bi-O2 layer.
1. Introduction Bi, Pb and T1 as the nearest neighbours in the same row of the periodic table all play important role in the perovskite structures of the newly discovered high Tc superconducting systems: B i - S r - C a - C u - O [ 1 ], B i - P b - S r - C a - C u - O [ 2 ], T I - B a - C a - C u - O [ 3 ], T1P b - S r - C a - C u - O [ 4 ] and P b - L n - S r - C a - C u - O [ 5 ] (Ln = rare earth element). Their electronic structure and ionic size appear to be in favour to the formation of the layered structures. It has been found that a portion if Bi 5+ present B i - S r - C a - C u - O when treated in strong oxidising atmosphere depressed the T¢ dramatically [ 6 ]. Pb substitution for Bi stabilised the 110 K phase [ 7 ]. A zero resistance at 107 K was achieved for Pb stabilised samples. Po2 shows little effect on T¢ with the maximum variation of zero resistance temperature 2-3 K in Pb substituted samples while a large variation in T~ with Po2 was observed for Bi-based materials without Pb substitution. The stabilisation of the 110 K phase by Pb substitution may be the consequence of the reduction of the charge states of Bi. It would be expected that as Sb is a nearest neighbour in the same column as Bi in the periodic table Sb 5+ should be more stable than Bi 5+. Thus substitution of Sb 5+ for Bi 3+ will increase the concentra-
tion of valence 5 + state in the Bi-O layers, and the Tc will be affected. However a large enhancement in Tc by substituting for Bi has been reported by Liu et al. [ 8 ] who have observed a zero resistance at 134 K for a Sb substituted sample. In this paper we report the effects produced by substituting Sb 5+ (Sb205) for Bi 3+ ( B i 2 0 3) on the properties in B i - P b - S r - C a - C u - O systems. These results show that when more oxygen is introduced, the superconducting transition becomes sensitive to oxygen pressures, particular in higher oxygen pressure, contrary to the Pb stabilised Bi-based materials. It is also found that the superconductivity anticorrelates to Cu 3+ concentration, which is critical in other superconductors [ 9 ], indicating that the superconductivity involves essentially Cu 2+ - O 2bands.
2. Experimental The samples were prepared by both standard solid state reaction and co-decomposition of the mixture prepared by drying a solution of Bi, Sr, Ca, Cu and Pb nitrates and then mixing with Sb205, calcining at 800°C for 12 h, at 840°C for 24 h, and pressing and sintering at 850°C for 60-100 h in different atmospheres from 1.0 to 0.01 arm ofpo in N2 and 02 mix-
0921-4534/89/$03.50 © Elsevier Science Publishers B.V. ( North-Holland Physics Publishing Division )
98
S.X. Dou et al. / Sb substitution in B i - P b - S r - C a - C u - O systems
ture. Furnace cooling or quenching were used in order to examine the effect on To. The electrical resistance was measured by the standard four probe DC technique with computer data logging. Microstructural and compositional studies were performed with JEOL JSM 840 scanning electron microscope (SEM) JEOL 2000 FX transmission electron microscopy (TEM) equipped with Link Systems energy dispersive spectrometer. TEM specimens were prepared by grinding the bulk materials with a mortar and pestle and collecting from a suspension in methanol onto a carbon film supported on an aluminium grid. X-ray diffraction patterns were obtained from a Philips type PW 1140/00 powder diffractiometer with C u K a radiation. The concentrations of labile ions Cu 3+ and the associated oxygen content were determined by the volumetric measurement technique [ 9 ].
O~
0 0 0
,
i~"
c
CO
o
b
3. R e s u l t s and d i s c u s s i o n I
45
Fig. 1 shows the temperature dependence of the voltage drop (as a measure of resistivity) for samples of nominal composition Bio.sPbo.2Sbo.o~SrCaC u 2 0 5 . 7 2 5 +y. These samples were heat treated under the same conditions: at 850°C in air for 100 h. It is seen that the Sb addition depressed Tc showing transitions at 107 K and 93 K for sample with x = 0 . 0 5 compared with Tc = 108 K for sample without Sb addition. X-ray diffraction patterns (fig. 2) show that peaks shift systematically to higher angles due to the
"•1 4>1
1 ° u u u u •
0
O0
0 o •
Q.ee
80
o
0000 0o
O °
~o
T (K)
12o
Fig. 1. Effect of Sb doping on Tc in Bi-Pb-Sr-Ca-Cu-O
160
I
I
I
I
I
35
I
i
I
I
25
I
[
I
I
15
I
a
I
I
I
5
2e
Fig. 2. X-ray diffraction patterns for Sb doped (a) and undoped (b) Bi-Pb-Sr-Ca-Cu-O.
Sb addition resulting in a reduction of unit cell parameters: a=0.526, b=0.523 and c=3.645 for undoped sample and a = 0.523, b = 0.518 and c = 3.598 for Sb added sample ( x = 0 . 0 5 ) . This decrease of parameters indicates that Sb was indeed introduced into the lattice structure. Since Sb 5+ should have a smaller radius than Bi s+ or Bi 3+, a reduction of unit cell parameters is expected upon substitution. The volume of the unit cell decreases continuously with sintering time up to 120 h (fig. 3) and then maintains constant indicating a slow process of the substitution. All peaks of the X-ray diffraction patterns can be indexed with the parameters given above except for peaks at 20=30.6% 30.8 ° and 41.7 ° which are due to the impurity phase SrCaCu406 (0114). This is consistent with SEM analysis results, which show a multiphase assemblage with (2223) as a major phase. With Sb doping TEM diffraction patterns in the (001) zone (fig. 4a) showed that the superlattice diffraction patterns in (½ kl) disappeared and the intensity of the superlattice diffraction decreased. This suggests that Sb 5+ substitution for Bi 3+ or Bi 5+
S.X. Dou et al. / S b substitution in B i - P b - S r - C a - C u - O systems
99
a D
o
,.526
G []
O
D
o
D
E
.522
E o
0
n.
0
°
•
0
,.518
Ii
¢
50
i
I
I
o
onneah~cj
I
time (h)
Fig. 3. Variations in unit cell parameters in Sb-doped Bil.6Pbo.4Sr2Ca2Cu3Ox, ( ~ ) undoped sample.
results in a relief of the strain modulation owing to the small size of Sb 5÷. Furthermore no other Sb-contained phases were observed by TEM confirming that Sb was substituted into the (2223) or (2212) lattice. Fig. 5 shows the temperature dependence of the voltage drop for samples with nominal composition of BioaPbo2Sbo.osSrCaCu2Os.72s+y treated under various oxygen partial pressures. It can be seen that the superconducting transition temperature for the sample treated in pure oxygen was largely depressed with zero resistance temperature below 77 K, whereas no effect of Sb addition on Tc was observed for the sample treated within the range of oxygen partial pressures from 0.05 to 0.01 atm. The sample which was quenched from 860 °C onto copper plate showed a semiconductor behaviour and a broad transition with onset temperature at 107 K and zero resistance temperature below 77 K. In contrast to the previous reports [8 ] no superconducting transition higher than 110 K was detected. In fact when Sb content increases from 0.05 to 0.1 the superconducting transition was largely depressed. The Cu 3+ concentration and the associated oxygen content as determined by volumetric measurement technique for samples treated under different Po2 are listed in table I. We see that the extra oxygen and Cu 3÷ concentration were depressed by Sb addition compared with those undoped materials. This indicates that Sb is in the pentavalent state. Furthermore the extra oxygen content decreased slightly
b
I
Fig. 4. Superlattices observed in the (001) plane for Sb doped (a) and undoped (2223) (b).
with the decrease of oxygen pressure while the superconducting transition temperatures for samples treated under low oxygen pressure (0.01 to 0.05 arm) maintain unaffected by Sb addition in comparison with the undoped B i - P b - S r - C a - C u - O . This suggests that the Cu 3+ and the associated oxygen, critical to the superconductivity in YBa2Cu307 (123), are not important for sustaining the superconductivity in Bi-based superconductors. Thus the superconductivity for Bi-based materials occurs in Cu-O2 plane based on Cu 2+. In the B i - S r - C a - C u - O system we found that Tc
1O0
S.X. Dou et al. / Sb substitution in B i - P b - S r - C a - C u - O systems ov
vuo
0 0
"~
o°
o 00
07000 so
ee~
o o o o u 000(~0e00 0 ° e ee
in low oxygen pressure m a y be a t t r i b u t e d to partial reduction o f Sb 5+ with a reduction o f the extra oxygen content in Bi-O2 layers resulting in an imp r o v e m e n t o f c o n d u c t i o n in these layers. T h e r m o d y n a m i c calculations o b t a i n e d with the t h e r m o d a t a system [ 11 ] shows that Sb205 is stable in pure oxygen up to 1000 ° C, while Sb205 is in equil i b r i u m with 5b203 at 860°C (i.e. sintering temperature) in 0.01 a t m o f oxygen. Thus it is expected that the extra oxygen in Bi-O2 layer is reduced due to the reduction o f high o x i d a t i o n state ions u n d e r low oxygen pressure.
O0
oO:..-
@ oO
00°00
O" .ff l T (K)
~o
'
'
'
160
Fig. 5. Effect of Po2 on Tc in Sb-doped Bi-Pb-Sr-Ca-Cu-O.
4. Conclusion was largely depressed when sample was treated in pure oxygen. We attribute this depression to the presence o f Bi 5+ a n d associated extra oxygen in B i 02 layers, which t e n d to enlarge the B i - B i separation a n d increase resistance in these layers [ 10]. The consequence o f Sb substitution for Bi is to increase the concentration o f ions with pentavalence. This explains the depression o f T~ by Sb substitution for samples treated in pure oxygen where Sb 5+ is stable. N o effect o f Sb substitution on T~ for samples treated
In s u m m a r y Sb can be d o p e d into the superconducting phase and appears to be pentavalent, as evid e n c e d by the reduction o f unit cell p a r a m e t e r s a n d the decrease o f Cu 3÷ concentration. Sb substitution depresses Tc for samples treated in pure oxygen but not for samples treated u n d e r low oxygen pressure. This m a y be a t t r i b u t e d to the presence o f high oxid a t i o n state ions in Bi-O2 layer. Cu 3÷ concentration was depressed while Tc showed an anticorrelation to
Table I Superconducting transition temperatures and oxygen content in Sb doped Bi-Pb-Sr-Ca-Cu-O. Oxygen pressure
Tc midpoint
To zero resistance
y see formula
Cu3+% of total Cu
0.054 +0.002
5.4
Po2
BiSrCaCu2Os.5+y 1.0
90
< 77
Bio.sPbo.2SrCaCu2Os.6+y 1.0
105
103
0.05
5.0
Bio.sPbo.2Sbo.osSrCaCu2Os.725 +y
1.0 0.21 0.067 0.05 0.01 quenched from air
105 98 98 106 105 90
<77 86 88 103 102 < 77
0.036 0.035 0.031 0.031 0.03 0.021
3.6 3.5 3.1 3.1 3.0 2.1
S.X. Dou et aL / Sb substitution in B i - P b - S r - C a - C u - O systems
C u 3+ c o n c e n t r a t i o n , i n d i c a t i n g C u 3+ is n o t critical to s u p e r c o n d u c t i v i t y in B i - b a s e d materials. T h u s the C u - O 2 p l a n e b a s e d o n C u 2+ is r e s p o n s i b l e for t h e superconductivity.
Acknowledgements W e are grateful to M e t a l M a n u f a c t u r e s Ltd. for s u p p o r t ( S . X . D ) a n d also to t h e C o m m o n w e a l t h D e p a r t m e n t o f Industry, T e c h n o l o g y a n d C o m m e r c e (H.K.L).
References [ 1 ] H. Maeda, Y. Tanaka, M. Fukutomi and T. Asano, Jpn. Appl. Phys. 27 (1988) 209. [2] H.K. Liu, S.X. Dou, N. Sawides, J.P. Zhou, N.X. Tan, A.J. Bourdillon, M. Kviz and C.C. Sorrell, Physica C 157 (1989) 93. [3] Z.Z. Sheng and A.M. Hermann, Nature 332 (1988) 138.
101
[4] M.A. Subramanian, C.C. Torardi, J. Gopalakrishnan, P.L. Gci, J.C. Calabrese, T.R. Askew, R.B. Flippen and A.W. Sleight, Science 242 (1988) 249. [5] R.J. Cava, B. Batlogg, J.J. Krajewski, L.W. Rupp, L.F. Sehneemeyer, T. Siegrist, R.B. van Dover, P. Marsh, W.F. Peck, Jr., P.K. Gallagher, S.H. Glarum, J.H. Marshall, R.C. Farrow, J.C. Waszczak, R. Hull and P. Trevor, Nature 336 (1988) 211. [6] S.X. Dou, H.K. Liu, A.J. Bourdillon, M. Kviz, N.X. Tan and C.C. Sorrell, The Stability of Superconducting Phases in Bi-Sr-Ca-Cu-O and the Role of Pb Doping, submitted to Phys. Rev. B. [7] H.K. Liu, S.X. Dou, N. Sawides, J.P. Zhou, N.X. Tan, A.J. Bourdillon, M. Kviz and C.C. Sorrell, Mater. Sci. Forum 34-36 (1988) 309. [8] H.B. Liu, L.Z. Cao, L. Zhou, Z.Q. Mao, W.J. Zhang, X.X. Liu, Z.D.Y.B. Xue, X.L. Mao, G. Zhou, Y.Z. Ruan, Z.J. Chen and Y.H. Zhang, Zero Resistance at 132 K in the Multiphase k System Bil.9_xPbxSbo.tSr2Ca2Cu3Oy with x=0.3, 0.4. Preprim. [9] S.X. Dou, H.K. Liu, A.J. Bourdillon, N. Sawides, J.P. Zhou and C.C. Sorrell, Solid State Commun. 68 (1988) 221. [ 10] H.W. Zandbergen, W.H. Groen and I.C. Mijlhoff, Physica C 156 (1988) 325. [ l l ] A . G . Turnbull and M.W. Wadesley, 1987 Thermodata System Version CSIRO, Port Melbourne, Victoria, Australia.
EFFECT OF Sb S U B S T I T U T I O N O N Tc IN B i - P b - S r - C a - C u - O SYSTEMS S.X. DOU, H.K. LIU, N.X. TAN, Y.J. SHENG and W.K. JONES ~ School of Materials Science and Engineering, University of New South Wales, P.O. Box 1, Kensington, N S W 2033, Australia College of Engineering and Applied Science, The State University o f Florida at Miami, VH134 Miami, FL 33199, USA Received 9 February 1989
The oxidation states and thereby oxygen non-stoichiometry in B i - S r - C a - C u - O systems have been found to be an important factor for superconductivity. Sb has been doped into B i - P b - S r - C a - C u - O and appears to be pentavalent as evidenced by the reduction of unit cell parameters, and the decrease of Cu 3+ concentration. Sb substitution up to 5% Bi and Pb depressed Tc for sample treated in pure oxygen but not under low oxygen pressure. Cu 3+ is not critical to superconductivity in Bi-based materials as it is in YBa2Cu3OT. The Cu-O2 plane based on Cu 2+ is responsible for sustaining the high T¢. No superconducting phases other than (Bi, Pb, Sb)2Sr2CaCu2Ox (2212) and (Bi, Pb, Sb)zSr2Ca2Cu3Ox (2223) were detected contrary to previous report. Sb doping weakens the superlattice considerably due to relief of the strain in Bi-O2 layer.
1. Introduction Bi, Pb and T1 as the nearest neighbours in the same row of the periodic table all play important role in the perovskite structures of the newly discovered high Tc superconducting systems: B i - S r - C a - C u - O [ 1 ], B i - P b - S r - C a - C u - O [ 2 ], T I - B a - C a - C u - O [ 3 ], T1P b - S r - C a - C u - O [ 4 ] and P b - L n - S r - C a - C u - O [ 5 ] (Ln = rare earth element). Their electronic structure and ionic size appear to be in favour to the formation of the layered structures. It has been found that a portion if Bi 5+ present B i - S r - C a - C u - O when treated in strong oxidising atmosphere depressed the T¢ dramatically [ 6 ]. Pb substitution for Bi stabilised the 110 K phase [ 7 ]. A zero resistance at 107 K was achieved for Pb stabilised samples. Po2 shows little effect on T¢ with the maximum variation of zero resistance temperature 2-3 K in Pb substituted samples while a large variation in T~ with Po2 was observed for Bi-based materials without Pb substitution. The stabilisation of the 110 K phase by Pb substitution may be the consequence of the reduction of the charge states of Bi. It would be expected that as Sb is a nearest neighbour in the same column as Bi in the periodic table Sb 5+ should be more stable than Bi 5+. Thus substitution of Sb 5+ for Bi 3+ will increase the concentra-
tion of valence 5 + state in the Bi-O layers, and the Tc will be affected. However a large enhancement in Tc by substituting for Bi has been reported by Liu et al. [ 8 ] who have observed a zero resistance at 134 K for a Sb substituted sample. In this paper we report the effects produced by substituting Sb 5+ (Sb205) for Bi 3+ ( B i 2 0 3) on the properties in B i - P b - S r - C a - C u - O systems. These results show that when more oxygen is introduced, the superconducting transition becomes sensitive to oxygen pressures, particular in higher oxygen pressure, contrary to the Pb stabilised Bi-based materials. It is also found that the superconductivity anticorrelates to Cu 3+ concentration, which is critical in other superconductors [ 9 ], indicating that the superconductivity involves essentially Cu 2+ - O 2bands.
2. Experimental The samples were prepared by both standard solid state reaction and co-decomposition of the mixture prepared by drying a solution of Bi, Sr, Ca, Cu and Pb nitrates and then mixing with Sb205, calcining at 800°C for 12 h, at 840°C for 24 h, and pressing and sintering at 850°C for 60-100 h in different atmospheres from 1.0 to 0.01 arm ofpo in N2 and 02 mix-
0921-4534/89/$03.50 © Elsevier Science Publishers B.V. ( North-Holland Physics Publishing Division )
98
S.X. Dou et al. / Sb substitution in B i - P b - S r - C a - C u - O systems
ture. Furnace cooling or quenching were used in order to examine the effect on To. The electrical resistance was measured by the standard four probe DC technique with computer data logging. Microstructural and compositional studies were performed with JEOL JSM 840 scanning electron microscope (SEM) JEOL 2000 FX transmission electron microscopy (TEM) equipped with Link Systems energy dispersive spectrometer. TEM specimens were prepared by grinding the bulk materials with a mortar and pestle and collecting from a suspension in methanol onto a carbon film supported on an aluminium grid. X-ray diffraction patterns were obtained from a Philips type PW 1140/00 powder diffractiometer with C u K a radiation. The concentrations of labile ions Cu 3+ and the associated oxygen content were determined by the volumetric measurement technique [ 9 ].
O~
0 0 0
,
i~"
c
CO
o
b
3. R e s u l t s and d i s c u s s i o n I
45
Fig. 1 shows the temperature dependence of the voltage drop (as a measure of resistivity) for samples of nominal composition Bio.sPbo.2Sbo.o~SrCaC u 2 0 5 . 7 2 5 +y. These samples were heat treated under the same conditions: at 850°C in air for 100 h. It is seen that the Sb addition depressed Tc showing transitions at 107 K and 93 K for sample with x = 0 . 0 5 compared with Tc = 108 K for sample without Sb addition. X-ray diffraction patterns (fig. 2) show that peaks shift systematically to higher angles due to the
"•1 4>1
1 ° u u u u •
0
O0
0 o •
Q.ee
80
o
0000 0o
O °
~o
T (K)
12o
Fig. 1. Effect of Sb doping on Tc in Bi-Pb-Sr-Ca-Cu-O
160
I
I
I
I
I
35
I
i
I
I
25
I
[
I
I
15
I
a
I
I
I
5
2e
Fig. 2. X-ray diffraction patterns for Sb doped (a) and undoped (b) Bi-Pb-Sr-Ca-Cu-O.
Sb addition resulting in a reduction of unit cell parameters: a=0.526, b=0.523 and c=3.645 for undoped sample and a = 0.523, b = 0.518 and c = 3.598 for Sb added sample ( x = 0 . 0 5 ) . This decrease of parameters indicates that Sb was indeed introduced into the lattice structure. Since Sb 5+ should have a smaller radius than Bi s+ or Bi 3+, a reduction of unit cell parameters is expected upon substitution. The volume of the unit cell decreases continuously with sintering time up to 120 h (fig. 3) and then maintains constant indicating a slow process of the substitution. All peaks of the X-ray diffraction patterns can be indexed with the parameters given above except for peaks at 20=30.6% 30.8 ° and 41.7 ° which are due to the impurity phase SrCaCu406 (0114). This is consistent with SEM analysis results, which show a multiphase assemblage with (2223) as a major phase. With Sb doping TEM diffraction patterns in the (001) zone (fig. 4a) showed that the superlattice diffraction patterns in (½ kl) disappeared and the intensity of the superlattice diffraction decreased. This suggests that Sb 5+ substitution for Bi 3+ or Bi 5+
S.X. Dou et al. / S b substitution in B i - P b - S r - C a - C u - O systems
99
a D
o
,.526
G []
O
D
o
D
E
.522
E o
0
n.
0
°
•
0
,.518
Ii
¢
50
i
I
I
o
onneah~cj
I
time (h)
Fig. 3. Variations in unit cell parameters in Sb-doped Bil.6Pbo.4Sr2Ca2Cu3Ox, ( ~ ) undoped sample.
results in a relief of the strain modulation owing to the small size of Sb 5÷. Furthermore no other Sb-contained phases were observed by TEM confirming that Sb was substituted into the (2223) or (2212) lattice. Fig. 5 shows the temperature dependence of the voltage drop for samples with nominal composition of BioaPbo2Sbo.osSrCaCu2Os.72s+y treated under various oxygen partial pressures. It can be seen that the superconducting transition temperature for the sample treated in pure oxygen was largely depressed with zero resistance temperature below 77 K, whereas no effect of Sb addition on Tc was observed for the sample treated within the range of oxygen partial pressures from 0.05 to 0.01 atm. The sample which was quenched from 860 °C onto copper plate showed a semiconductor behaviour and a broad transition with onset temperature at 107 K and zero resistance temperature below 77 K. In contrast to the previous reports [8 ] no superconducting transition higher than 110 K was detected. In fact when Sb content increases from 0.05 to 0.1 the superconducting transition was largely depressed. The Cu 3+ concentration and the associated oxygen content as determined by volumetric measurement technique for samples treated under different Po2 are listed in table I. We see that the extra oxygen and Cu 3÷ concentration were depressed by Sb addition compared with those undoped materials. This indicates that Sb is in the pentavalent state. Furthermore the extra oxygen content decreased slightly
b
I
Fig. 4. Superlattices observed in the (001) plane for Sb doped (a) and undoped (2223) (b).
with the decrease of oxygen pressure while the superconducting transition temperatures for samples treated under low oxygen pressure (0.01 to 0.05 arm) maintain unaffected by Sb addition in comparison with the undoped B i - P b - S r - C a - C u - O . This suggests that the Cu 3+ and the associated oxygen, critical to the superconductivity in YBa2Cu307 (123), are not important for sustaining the superconductivity in Bi-based superconductors. Thus the superconductivity for Bi-based materials occurs in Cu-O2 plane based on Cu 2+. In the B i - S r - C a - C u - O system we found that Tc
1O0
S.X. Dou et al. / Sb substitution in B i - P b - S r - C a - C u - O systems ov
vuo
0 0
"~
o°
o 00
07000 so
ee~
o o o o u 000(~0e00 0 ° e ee
in low oxygen pressure m a y be a t t r i b u t e d to partial reduction o f Sb 5+ with a reduction o f the extra oxygen content in Bi-O2 layers resulting in an imp r o v e m e n t o f c o n d u c t i o n in these layers. T h e r m o d y n a m i c calculations o b t a i n e d with the t h e r m o d a t a system [ 11 ] shows that Sb205 is stable in pure oxygen up to 1000 ° C, while Sb205 is in equil i b r i u m with 5b203 at 860°C (i.e. sintering temperature) in 0.01 a t m o f oxygen. Thus it is expected that the extra oxygen in Bi-O2 layer is reduced due to the reduction o f high o x i d a t i o n state ions u n d e r low oxygen pressure.
O0
oO:..-
@ oO
00°00
O" .ff l T (K)
~o
'
'
'
160
Fig. 5. Effect of Po2 on Tc in Sb-doped Bi-Pb-Sr-Ca-Cu-O.
4. Conclusion was largely depressed when sample was treated in pure oxygen. We attribute this depression to the presence o f Bi 5+ a n d associated extra oxygen in B i 02 layers, which t e n d to enlarge the B i - B i separation a n d increase resistance in these layers [ 10]. The consequence o f Sb substitution for Bi is to increase the concentration o f ions with pentavalence. This explains the depression o f T~ by Sb substitution for samples treated in pure oxygen where Sb 5+ is stable. N o effect o f Sb substitution on T~ for samples treated
In s u m m a r y Sb can be d o p e d into the superconducting phase and appears to be pentavalent, as evid e n c e d by the reduction o f unit cell p a r a m e t e r s a n d the decrease o f Cu 3÷ concentration. Sb substitution depresses Tc for samples treated in pure oxygen but not for samples treated u n d e r low oxygen pressure. This m a y be a t t r i b u t e d to the presence o f high oxid a t i o n state ions in Bi-O2 layer. Cu 3÷ concentration was depressed while Tc showed an anticorrelation to
Table I Superconducting transition temperatures and oxygen content in Sb doped Bi-Pb-Sr-Ca-Cu-O. Oxygen pressure
Tc midpoint
To zero resistance
y see formula
Cu3+% of total Cu
0.054 +0.002
5.4
Po2
BiSrCaCu2Os.5+y 1.0
90
< 77
Bio.sPbo.2SrCaCu2Os.6+y 1.0
105
103
0.05
5.0
Bio.sPbo.2Sbo.osSrCaCu2Os.725 +y
1.0 0.21 0.067 0.05 0.01 quenched from air
105 98 98 106 105 90
<77 86 88 103 102 < 77
0.036 0.035 0.031 0.031 0.03 0.021
3.6 3.5 3.1 3.1 3.0 2.1
S.X. Dou et aL / Sb substitution in B i - P b - S r - C a - C u - O systems
C u 3+ c o n c e n t r a t i o n , i n d i c a t i n g C u 3+ is n o t critical to s u p e r c o n d u c t i v i t y in B i - b a s e d materials. T h u s the C u - O 2 p l a n e b a s e d o n C u 2+ is r e s p o n s i b l e for t h e superconductivity.
Acknowledgements W e are grateful to M e t a l M a n u f a c t u r e s Ltd. for s u p p o r t ( S . X . D ) a n d also to t h e C o m m o n w e a l t h D e p a r t m e n t o f Industry, T e c h n o l o g y a n d C o m m e r c e (H.K.L).
References [ 1 ] H. Maeda, Y. Tanaka, M. Fukutomi and T. Asano, Jpn. Appl. Phys. 27 (1988) 209. [2] H.K. Liu, S.X. Dou, N. Sawides, J.P. Zhou, N.X. Tan, A.J. Bourdillon, M. Kviz and C.C. Sorrell, Physica C 157 (1989) 93. [3] Z.Z. Sheng and A.M. Hermann, Nature 332 (1988) 138.
101
[4] M.A. Subramanian, C.C. Torardi, J. Gopalakrishnan, P.L. Gci, J.C. Calabrese, T.R. Askew, R.B. Flippen and A.W. Sleight, Science 242 (1988) 249. [5] R.J. Cava, B. Batlogg, J.J. Krajewski, L.W. Rupp, L.F. Sehneemeyer, T. Siegrist, R.B. van Dover, P. Marsh, W.F. Peck, Jr., P.K. Gallagher, S.H. Glarum, J.H. Marshall, R.C. Farrow, J.C. Waszczak, R. Hull and P. Trevor, Nature 336 (1988) 211. [6] S.X. Dou, H.K. Liu, A.J. Bourdillon, M. Kviz, N.X. Tan and C.C. Sorrell, The Stability of Superconducting Phases in Bi-Sr-Ca-Cu-O and the Role of Pb Doping, submitted to Phys. Rev. B. [7] H.K. Liu, S.X. Dou, N. Sawides, J.P. Zhou, N.X. Tan, A.J. Bourdillon, M. Kviz and C.C. Sorrell, Mater. Sci. Forum 34-36 (1988) 309. [8] H.B. Liu, L.Z. Cao, L. Zhou, Z.Q. Mao, W.J. Zhang, X.X. Liu, Z.D.Y.B. Xue, X.L. Mao, G. Zhou, Y.Z. Ruan, Z.J. Chen and Y.H. Zhang, Zero Resistance at 132 K in the Multiphase k System Bil.9_xPbxSbo.tSr2Ca2Cu3Oy with x=0.3, 0.4. Preprim. [9] S.X. Dou, H.K. Liu, A.J. Bourdillon, N. Sawides, J.P. Zhou and C.C. Sorrell, Solid State Commun. 68 (1988) 221. [ 10] H.W. Zandbergen, W.H. Groen and I.C. Mijlhoff, Physica C 156 (1988) 325. [ l l ] A . G . Turnbull and M.W. Wadesley, 1987 Thermodata System Version CSIRO, Port Melbourne, Victoria, Australia.