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Superconductivity in the system (Y, Ca, Sr) (Ba, Sr)2 (Cu3−z(SO4)zOx
Physica C 213 (1993) 14-16 North-Holland
Superconductivity in the system (Y, Ca, St) (Ba, Sr)2 (Cu3- z(SO4) zOx P.R. Slater
a, C. G r e a v e s a, M. Slaski b and C.M. M u i r h e a d b
a School of Chemistry, University of Birmingham, Birmingham B15 2TT, UK b School of Physics and Space Research, University of Birmingham, Birmingham B 15 2T E, UK
Received 29 March 1993 Revised manuscript received 18 May 1993
The effects of partial substitution of Ba for Sr on the superconducting transition in the sulphate containing materials [Yo.~4Cao.~rSro.l]Sr2Cu2.Ts(SO4)o.2206.12and [Yo.s4Sro.j61Sr2Cu2,~s(SO4)o.2206.12have been investigated. As the Ba content was increased, the superconductingtransitions becamesharper and Tcon,~tincreased to reach a maximumof 78 K. The cell symmetry was also observedto change from orthorhomhicto tetragonal, which is thought to be associated with randomization of the orientations of the sulphate groupsin the structure.
1. Introduction
Although the high pressure synthesis of YSr2Cu307 has been reported [ 1 ], stabilization by cation substitutions in the "chain" Cu sites is required for ambient pressure synthesis of such Ba-free analogues of YBa2Cu307 [2-4]. The stabilization of this system by partial CO 2- substitution for the "chain" Cu sites has also been reported [ 5 ], and in a previous paper we reported a similar stabilization by partial substitution of sulphate or phosphate on these sites, i.e. YSr2Cu3_~(XO4)zOy ( X = S , P; 0.2_
2. E x p e r i m e n t a l
High purity Y203, Y2(SO4)3.8H20, SrCO3, BaCO3, and CuO were used to prepare a range of samples, [Yo.74Cao.16Sro.l]SrECU2.78(SO4)o.EEOyand [Yo.a4Sro.16]Sr2Cu2.78(SO4)o.22Oy, with varying Ba contents (0 _
0921-4534/93/$06.00 © 1993 ElsevierScience Publishers B.V. All rights reserved.
P.R. Slater et al. /Superconductivity in (Y, Ca, Sr)(Ba, Sr)2Cu~_/SO,)~O~
tivity and susceptibility measurements and a DC SQUID magnetometer.
80
oooooooooooooo
60
3. Results and discussion
c
The unit cell parameters and superconducting onset temperatures (from AC susceptibility data) for a range of samples are shown in figs. 1 and 2. Figure 3 shows susceptibility and resistivity plots for [ Yo.74Cao.~6Sro.l ] SrBaCu2.7s (SO4)
15
40
[AC Susceptibility]
.~ 20 []
< O0
•
O0
0000
~O000
while t h e
0.2206.12,
powder X-ray diffraction pattern for this phase is shown in fig. 4. As Ba was gradually exchanged for Sr in [Yo.74Cao.16Sro.l ]Sr2_xBaxCu2.78(SO4)0.2206.12, 3.88
the
-20
40
50
60
70
80
90
Temperature/K
Fig. 3. AC susceptibility and [ Yo.74Cao.| 6Sro.1] SrBaCu2.7 a ( SO4 ) 0.2206. | 2'
resistivity
of
12.0
11.5
.~
j
3.86
_g o
11.0
3.84 10.5
3.82 0.00
0.25
0.50
0.75
E O O
!
10.0
i
i
1.00
1.25
1.50
10
Ba content (x)
30
50
70
20 (o)
Fig. I. Variation of unit cell [ Yo.74Cao.16Sro.1] Sr2 -xBaxCu2.Ts (SO4)0.2206.12.
lengths
in
Fig. 4. X-ray powder diffraction (CuKth) [Yo.74Cao.16Sro.l]SrBaCu2.Ts(SO4)0.2206.,2-
trace
of
80
70 ~--- 50 c 0
~ 5o I40 3O 0.00
i
i
i
i
i
0.25
0.50
0.75
1.00
1.25
Ba c o n t e n t
(x)
Fig. 2. Variation of T ~ o ~ with Ba content.
1,50
unit cell expanded and the cell symmetry was found to change from orthorhombic to tetragonal between x = 0 . 0 and x=0.5, see fig. 1. The partial substitution of Ba for Sr in related systems has previously been observed to result in similar changes in cell symmetry [7,8 ]. Our initial report of superconductivity in (Y, C a ) S r 2 C u 3 _ z ( S O 4 ) z O y , which included a preliminary structure refinement, suggested that the orthorhombicity was related to the orientation of the sulphate groups [ 6 ], and it therefore appears as if Ba doping induces orientational disorder of these oxyanions. This is supported by the observation that the carbonate groups in Sr2CuO2CO3 are subject to just such a randomization when Sr is partially replaced
16
P.R. Slater et al. / Superconductivity in (Y, Ca, Sr)(Ba, Sr)eCu~_z(SO4)zOx
by Ba [ 9,10 ]. The origin of this effect in Sr2CuO2CO 3 has been attributed to the presence of a statistical distribution of Ba on the Sr sites, and the greater size of Ba giving enhanced interactions with the O atoms of the CO3 groups [ l0 ]. The onset temperature for superconductivity was observed to increase with Ba content, reaching a maximum Tcon~t of 78 K for x = 1-1.5, see fig. 2. In addition to the increase in Tcon~t, significantly sharper transitions were observed, fig. 3. It should be noted that a similar variation of Tc with Ba content occurs in the parent YBa2_~SrxCu307 system [2, l 114 ], and it is also mirrored in the Yl_yCaySr2_xBaxCu2.aCro.207 system, in which part of the Cu in the Cu ( 1 ) site has been replaced by Cr [ 7 ]. For the latter system, it has been suggested that the variation may indicate that the optimum hole density for superconductivity may significantly vary with the Sr: Ba ratio [ 7 ]. A neutron diffraction study of these phases is planned for the near future.
Acknowledgement We thank the Science and Engineering Research Council for financial support.
References [ 1 ] B. Okai, Jpn. J. Appl. Phys. 29 (1990) L2180. [2] S.A. Sunshine, L.F. Schneemeyer, T. Siegrist, D.C. Douglass, J.V. Waszczak, R.J. Cava, E.M. Gyorgy and D.W. Murphy, Chem. Mater. 1 (1989) 331. [ 3 ] P.R. Slater and C. Greaves, Physica C 180 ( 1991 ) 299. [ 4 ] T. Den and T. Kobayashi, Physica C 196 (1992) 141. [ 5 ] Y. Miyazaki, H. Yamane, N. Ohnishi, T. Kajitani, K. Hiraga, Y. Morii, S. Funahashi and T. Hirai, Physica C 198 (1992) 7. [6] P.R. Slater, C. Greaves, M. Slaski and C.M. Muirhead, Physica C 208 (1993) 193. [7] T.G.N. Babu and C. Greaves, Physica C 207 (1992) 44. [ 8 ] T.G.N. Babu, J. Kilgour, P.R. Slater and C. Greaves, J. Solid State Chem., to be published. [ 9 ] C. Chaillout, Q. Huang, R.J. Cava, J. Chenavas, A. Santoro, P. Bordet, J.L. Hodeau, J.J. Krajewski, J.P. Levy, M. Marezio and W.F. Peck Jr., Physica C 195 (1992) 335. [ 10] A.R. Armstrong and P.P. Edwards, J. Solid State Chem. 98 (1992) 432. [ 11 ] A. Ono, T. Tanaka, H. Nozaki and Y. Ishizawa, Jpn. J. Appl. Phys. 26 (1987) L1687. [ 12 ] B.W. Veal, W.K. Kwok, A. Umezawa, G.W. Crabtree, J.D. Jorgensen, J.W. Downey, L.J. Nowicki, A.W. Mitchell, A.P. Paulikas and C.H. Sower, Appl. Phys. Lett. 51 (1987) 279. [ 13] P. Karen, H. FjeUvag, A. Kjekshus and A.F. Andresen, J. Solid State Chem. 92 ( 1991 ) 57. [ 14] A.K. Ganguli and M.A. Subramanian, Mater. Res. Bull. 26 ( 1991 ) 869.
Superconductivity in the system (Y, Ca, St) (Ba, Sr)2 (Cu3- z(SO4) zOx P.R. Slater
a, C. G r e a v e s a, M. Slaski b and C.M. M u i r h e a d b
a School of Chemistry, University of Birmingham, Birmingham B15 2TT, UK b School of Physics and Space Research, University of Birmingham, Birmingham B 15 2T E, UK
Received 29 March 1993 Revised manuscript received 18 May 1993
The effects of partial substitution of Ba for Sr on the superconducting transition in the sulphate containing materials [Yo.~4Cao.~rSro.l]Sr2Cu2.Ts(SO4)o.2206.12and [Yo.s4Sro.j61Sr2Cu2,~s(SO4)o.2206.12have been investigated. As the Ba content was increased, the superconductingtransitions becamesharper and Tcon,~tincreased to reach a maximumof 78 K. The cell symmetry was also observedto change from orthorhomhicto tetragonal, which is thought to be associated with randomization of the orientations of the sulphate groupsin the structure.
1. Introduction
Although the high pressure synthesis of YSr2Cu307 has been reported [ 1 ], stabilization by cation substitutions in the "chain" Cu sites is required for ambient pressure synthesis of such Ba-free analogues of YBa2Cu307 [2-4]. The stabilization of this system by partial CO 2- substitution for the "chain" Cu sites has also been reported [ 5 ], and in a previous paper we reported a similar stabilization by partial substitution of sulphate or phosphate on these sites, i.e. YSr2Cu3_~(XO4)zOy ( X = S , P; 0.2_
2. E x p e r i m e n t a l
High purity Y203, Y2(SO4)3.8H20, SrCO3, BaCO3, and CuO were used to prepare a range of samples, [Yo.74Cao.16Sro.l]SrECU2.78(SO4)o.EEOyand [Yo.a4Sro.16]Sr2Cu2.78(SO4)o.22Oy, with varying Ba contents (0 _
0921-4534/93/$06.00 © 1993 ElsevierScience Publishers B.V. All rights reserved.
P.R. Slater et al. /Superconductivity in (Y, Ca, Sr)(Ba, Sr)2Cu~_/SO,)~O~
tivity and susceptibility measurements and a DC SQUID magnetometer.
80
oooooooooooooo
60
3. Results and discussion
c
The unit cell parameters and superconducting onset temperatures (from AC susceptibility data) for a range of samples are shown in figs. 1 and 2. Figure 3 shows susceptibility and resistivity plots for [ Yo.74Cao.~6Sro.l ] SrBaCu2.7s (SO4)
15
40
[AC Susceptibility]
.~ 20 []
< O0
•
O0
0000
~O000
while t h e
0.2206.12,
powder X-ray diffraction pattern for this phase is shown in fig. 4. As Ba was gradually exchanged for Sr in [Yo.74Cao.16Sro.l ]Sr2_xBaxCu2.78(SO4)0.2206.12, 3.88
the
-20
40
50
60
70
80
90
Temperature/K
Fig. 3. AC susceptibility and [ Yo.74Cao.| 6Sro.1] SrBaCu2.7 a ( SO4 ) 0.2206. | 2'
resistivity
of
12.0
11.5
.~
j
3.86
_g o
11.0
3.84 10.5
3.82 0.00
0.25
0.50
0.75
E O O
!
10.0
i
i
1.00
1.25
1.50
10
Ba content (x)
30
50
70
20 (o)
Fig. I. Variation of unit cell [ Yo.74Cao.16Sro.1] Sr2 -xBaxCu2.Ts (SO4)0.2206.12.
lengths
in
Fig. 4. X-ray powder diffraction (CuKth) [Yo.74Cao.16Sro.l]SrBaCu2.Ts(SO4)0.2206.,2-
trace
of
80
70 ~--- 50 c 0
~ 5o I40 3O 0.00
i
i
i
i
i
0.25
0.50
0.75
1.00
1.25
Ba c o n t e n t
(x)
Fig. 2. Variation of T ~ o ~ with Ba content.
1,50
unit cell expanded and the cell symmetry was found to change from orthorhombic to tetragonal between x = 0 . 0 and x=0.5, see fig. 1. The partial substitution of Ba for Sr in related systems has previously been observed to result in similar changes in cell symmetry [7,8 ]. Our initial report of superconductivity in (Y, C a ) S r 2 C u 3 _ z ( S O 4 ) z O y , which included a preliminary structure refinement, suggested that the orthorhombicity was related to the orientation of the sulphate groups [ 6 ], and it therefore appears as if Ba doping induces orientational disorder of these oxyanions. This is supported by the observation that the carbonate groups in Sr2CuO2CO3 are subject to just such a randomization when Sr is partially replaced
16
P.R. Slater et al. / Superconductivity in (Y, Ca, Sr)(Ba, Sr)eCu~_z(SO4)zOx
by Ba [ 9,10 ]. The origin of this effect in Sr2CuO2CO 3 has been attributed to the presence of a statistical distribution of Ba on the Sr sites, and the greater size of Ba giving enhanced interactions with the O atoms of the CO3 groups [ l0 ]. The onset temperature for superconductivity was observed to increase with Ba content, reaching a maximum Tcon~t of 78 K for x = 1-1.5, see fig. 2. In addition to the increase in Tcon~t, significantly sharper transitions were observed, fig. 3. It should be noted that a similar variation of Tc with Ba content occurs in the parent YBa2_~SrxCu307 system [2, l 114 ], and it is also mirrored in the Yl_yCaySr2_xBaxCu2.aCro.207 system, in which part of the Cu in the Cu ( 1 ) site has been replaced by Cr [ 7 ]. For the latter system, it has been suggested that the variation may indicate that the optimum hole density for superconductivity may significantly vary with the Sr: Ba ratio [ 7 ]. A neutron diffraction study of these phases is planned for the near future.
Acknowledgement We thank the Science and Engineering Research Council for financial support.
References [ 1 ] B. Okai, Jpn. J. Appl. Phys. 29 (1990) L2180. [2] S.A. Sunshine, L.F. Schneemeyer, T. Siegrist, D.C. Douglass, J.V. Waszczak, R.J. Cava, E.M. Gyorgy and D.W. Murphy, Chem. Mater. 1 (1989) 331. [ 3 ] P.R. Slater and C. Greaves, Physica C 180 ( 1991 ) 299. [ 4 ] T. Den and T. Kobayashi, Physica C 196 (1992) 141. [ 5 ] Y. Miyazaki, H. Yamane, N. Ohnishi, T. Kajitani, K. Hiraga, Y. Morii, S. Funahashi and T. Hirai, Physica C 198 (1992) 7. [6] P.R. Slater, C. Greaves, M. Slaski and C.M. Muirhead, Physica C 208 (1993) 193. [7] T.G.N. Babu and C. Greaves, Physica C 207 (1992) 44. [ 8 ] T.G.N. Babu, J. Kilgour, P.R. Slater and C. Greaves, J. Solid State Chem., to be published. [ 9 ] C. Chaillout, Q. Huang, R.J. Cava, J. Chenavas, A. Santoro, P. Bordet, J.L. Hodeau, J.J. Krajewski, J.P. Levy, M. Marezio and W.F. Peck Jr., Physica C 195 (1992) 335. [ 10] A.R. Armstrong and P.P. Edwards, J. Solid State Chem. 98 (1992) 432. [ 11 ] A. Ono, T. Tanaka, H. Nozaki and Y. Ishizawa, Jpn. J. Appl. Phys. 26 (1987) L1687. [ 12 ] B.W. Veal, W.K. Kwok, A. Umezawa, G.W. Crabtree, J.D. Jorgensen, J.W. Downey, L.J. Nowicki, A.W. Mitchell, A.P. Paulikas and C.H. Sower, Appl. Phys. Lett. 51 (1987) 279. [ 13] P. Karen, H. FjeUvag, A. Kjekshus and A.F. Andresen, J. Solid State Chem. 92 ( 1991 ) 57. [ 14] A.K. Ganguli and M.A. Subramanian, Mater. Res. Bull. 26 ( 1991 ) 869.