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Superconductivity at 108 K in sulphur-substituted YBa2Cu3Ox
628
Journal of Crystal Growth 85 (1987) 628 631 North-Holland, Amsterdam
SUPERCONDUCTIVITY AT 108 K IN SULPHUR-SUBSTITUTED YEa 2Cu3O~ K.N.R. TAYLOR, D.N. MATITHEWS and G.J. RUSSELL Advanced Electronic Materials Group, School of Physics, University of New South Wales, Post Office Box 1, Kensington, NSW 2033, Australia
Received 17 September 1987; manuscript received in final form 26 September 1987
In an intensive series of investigations of the effects of elemental substitutional changes on the superconducting properties of YBa 2Cu 3O~~ we have recently studied the behaviour induced by sulphur substitution. All samples retained full superconducting transitions to 20% replacement of CuO by CuS and the 10% specimen showed a transition at 108 K. With repeated cycling, however, this degraded to 89 K at which it was stable.
1. Introduction One of the exciting features of the high temperature superconductors based qn YBa2Cu3O~ is that they are capable of extensive elemental substitution in a search for improved materials. Exhaustive studies have already been carried out by a number of research groups (see, for example, refs. [1 3]) for the case of partial or complete rare earth substitution. These have demonstrated interesting results although there has been no report of enhanced critical temperatures. Similarly, when barium is replaced with other alkaline earth metals, the overall trend is towards a continuous decrease in 7~[4]. It must be mentioned, however, that for strontium substitution, reports have recently been made of critical ternperatures close to and in excess of room temperature [5]. Copper, too, appears vital to maintaining superconducting behaviour at temperatures close to 100 K, as substitution of other transition metals has only achievedresults over ainsmall concentration range andbeen invariably eventual degradation of the resistive behaviour [6 8]. Oxygen concentration changes can be imposed by suitable thermal treatments in the range 400 600°C, and both nitrogen- and helium-induced effects are known at these temperatures [9 11]. These effects appear to be unrelated to the 0022-0248/87/$03.50 © Elsevier Science Publishers (North-Holland Physics Publishing Division)
remarkable changes which occur when either of these gases is introduced into the solid lattice at temperatures close to 77 K [12,13]. Despite these few indirect effects, however, there appears to have been little or no attempt to explore the quite extensive substitutional changes which can be made for the oxygen atoms in the various sites available in the orthorhombic perovskite structure. A number of reports using fluorine substitution suggest that these highly unstable materials may exhibit ill defined transitions to zero resistance near to 150 K [14]. One of the immediately obvious and relatively easily attained substitutions of this kind occurs through the replacement of oxygen by sulphur and in a recent series of measurements of this type we have observed a number of interesting results which are described below.
2. Results and discussion 5)~were prepared by YBa2Cu3(O, ourSamples normal of process of sintering a lightly pressed pellet of mixed compounds at 950°C for several hours followed by an extended annealing treatment at 550° during the final cool down [15]. In the present study, samples were made in which 3%, 10%, 20%, 50% and 100% of the CuO was substituted by CuS.
B.V.
K.N.R. Taylor et a!.
/ Superconductivity at 108 K in sulphur-substituted YBa2Cu3O,~
Visual inspection of the as-prepared samples for 3% and 10% substitution, after removal from the furnace, showed the presence of unusually large grains in the sample compared with those for the normal YBa 2Cu 3°x composition. The dimensions of these grains lay in the range 100—200 p~m and attempts are now being made to explore this effect as a basis for crystal growth. X-ray powder diffraction observations of the material showed that the orthorhombic phase dominated the structure for all except the 50% and 100% substituted samples. No measurable lattice parameter changes were observable (~2O 0.10) and the only significant change in the diffraction pattern was a very rapid variation of the (005) peak intensity at 38.4°, relative to either the principal (110/103) diffraction at 32.8°or the (113) peak at 40.4° as shown in fig. 1. Lee et al. [16] were the first to point out the sensitivity of this reflection to displacements of the barium atoms within the unit cell, a fact we have used to establish the nature of the structural differences between the YBa2Cu3O~ and Y2Ba3 Cu5O~compositions [17,18]. Assuming that the sulphur ions enter the lattice substitutionally at oxygen sites, then the observed dramatic changes in the intensity of the (005) reflection can occur either because of barium ion displacements towards the yttrium planes [15] or because of the increased X-ray scattering factor of sulphur compared with oxygen. Calculation of the structure factor suggests that the donunant mechanism is probably the one involving displacement of the barium ions. In view of the large crystallite growth, and the freedom from observed impurity phases in the diffraction pattern to quite large substitutional levels, we suggest that the addition of sulphur may serve to initiate and stabilize the orthorhombic lattice in these materials. Sample resistivities were measured using a conventional 4-probe configuration with a stabilized specimen current of 10 mA. Electrical contacts were made using Dolite silver paste. The specimen voltage was measured directly onto an XY recorder (Y-axis) while the thermocouple output was displayed on the X-axis which had previously been calibrated. The specimen current was monitored separately using a digital meter. All meas-
005
629
103
ito
013
106 113
________________________
40
35
31
2 e (degrees) Fig. 1. The region of the X-ray diffraction pattern containing the 005 reflection for the 3%, 10% and 20% samples showing the rapid change in relative intensity of this peak (3% at the top and 20% at the bottom).
urements were made as the temperature rose from 77 K to room temperature at a rate of 1 K/mm. The 3%, 10% and 20% samples all exhibited cornplete superconducting transitions; however, both 50% and 100% substitution of CuS for CuO resulted in semiconducting materials with room temperature resistance in excess of 106 Both the 3% and 20% samples exhibited critical temperatures close to those of the pure YBa 2Cu 3°x compound; however, the initial observational run on the 10% sample revealed a transition well in excess of 100 K, with an onset at 113.5 K and a final zero resistance (10 6 ~ cm) at 108 K, as shown in fig. 2a. Repeated cycling of all the samples, between ~,
/ Superconductivity at 108 K in sulphur-substituted YBa2Cu3O~
K.N.R. Taylor et al.
630
YBa2Cu3O~composition, at temperatures in excess of 100 K, appears to be a common feature
50 10’I
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20
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1.0
a
3’!. 0
so
~o
100
110
120
130
TEMPERATURE (K)
AT
I I
E
Cycle 2 Cycle 3 CYCI~
in LU
.yclel I
1135 98 91
108 95 89
I
~ I 30 2 0
Cyc ~
C~IeI
5
-
C
___________________________________________ 80 90 100 110 120 130
~
TEMPERATURE (K)
Fig. 2. (a) The temperature variation of the resistivity in the 3%, 10% and 20% substituted samples which exhibited a superconducting transition. The final critical temperatures obtained after cycling the 3% and 20% samples are indicated. (b) The degradation of the 108 K transition with repeated cycling between 77 and 300 K. The small transients shown in the normal state of the second cycle appear to be typical of unstable materials,
room temperature and 77 K, led to a continuous degradation in their performance, as shown in fig. 2b for the 10% material with a final transition (p = 0) occurring at 89 K after three cycles. Further cycling did not lower this temperature. Parts of the sample which had remained in the laboratory atmosphere for approximately 24 h were also degraded and exhibited transition temperatures of 86 K. The stable transition temperatures of the other samples after cycling are shown in fig. 2a. Attempts to restore the high temperature superconducting state by heating (300°C for 15 mm) and vacuum treatment (2 h at room temperature) both failed to have any significant effect on the deteriorated samples. This lack of stability of superconducting transitions which occur in materials based on the
of the materials themselves. There is some evidence theseindependent transitions of arethetoprecise be found in which isthat almost details overprocessed samples [19] or compositions in the Y203—BaO—CuO phase diagram lying close to the tie-line boundaries which define the existence region of the compound [20]. Consequently, it is tempting to identify the origin of the high temperature transitions with conditions which leave the crystal structure of the material close to the limits of its stability, as was suggested by Matthias in 1971 [21] in connection with niobium based materials. Whether this is so in the present case is unclear, particularly since the evidence of both the grain sizes and X-ray diffraction data suggest that
sulphur view improve the sample rapidthe deterioration lattice in the atmosphere itmay is ofmore likely that the stability. sulphur substitutionIn leaves the vulnerable to combined water vapour and carbon dioxide attack. No sulphate formation could be detected in our sampies by X-ray diffraction or optical microscopy. Further work is in progress to establish the location of the sulphur atoms in the lattice and their effect on the carrier concentration in the samples, in order to understand the role which this atomic substitution plays in the superconducting process.
References [11 P.H. Hor, R.L. Meng, Y.Q. Wang, L. Gao, Z.J. Huang, J. Bechtold, K. Forster and C.W. Chu, Phys. Rev. Letters 58 (1987) 1891. [2] S. Hosoya, M. Onoda, S. Shamoto and M. Sato, Japan. J. Appl. Phys. 26 (1987) L456. Yamada, K. Kinoshita, A. Matsuda, T. Watanabe and Y. Asano, Japan. J. Appi. Phys. 26 (1987) L706. [4] Appi. T. Wada, Adachi, Mihara and R. Inaba, Japan. J. Phys.S. 26 (1987) T. L706. [5] H. Ihara, N. Terada, J. Jo, M. Hirabayashi. M. Tokumoto, Y. Kimura, T. Matsubara and R. Suoise, Japan. J. Appi. Phys. 26 (1987) L1413. [o] J. Tian, L.L. Wang, B.Q. Zhang, X.M. Dai, J.L. Wang and G.G. Pan, in: Proc. Beijing High 7~Superconductor Conf., June 1987.
[31T.
[7] G. Xiao, F.H. Streitz, A. Gavrin, Y.W. Du and C.L.
Chien, Phys. Rev. B35 (1987) 8782.
K.N.R. Taylor eta!.
/ Superconductivity at 108 K in sulphur-substituted
[8] S. Bosi, K.N.R. Taylor and G.J. Russell, to be published. [9] R. Beyers, G. Lim, E.M. Engler, V.Y. Lee, M.L. Ramirez, R.J. Savoy and R.D. Jacowitz, Solid State Phys., submitted. [10] Y. Ito, H. Hasegawa, K. Takagi and K. Miyanchi, Japan. J. Appl. Phys. 26 (1987) L692. [11] P.K. Gallagher, Advan. Ceram. Mater. 2 (1987) 632. [12] D.N. Matthews, A. Bailey, T. Puzzer, G.J. Russell, j Cochrane, R.A. Vaile, H.B. Sun and K.N.R. Taylor, Solid State Commun., submitted. [131 D.N. Matthews, A. Bailey, R.A. Vaile, G.J. Russell and K.N.R. Taylor, Nature 328 (1987) 786. [14] SR. Ovshinsky, R.T. Young, D.D. Allred, G. De Maggio and GA. Van der Leeden, Phys. Rev. Letters 58 (1987) 2579. [15] K.N R. Taylor, High Temperature superconductors, AEM Report 69, UNSW, 1987.
YBa
2Cu3OA
631
[16] S.J. Lee, J.P. Golben, S.Y. Lee, X.D. Chen, Y. Song, T.W. Nob, RD. McMichael, Y. Cao, J. Testa, F. Zuo, JR. Gaines, A.J. Epstein, D.L. Cox, J.C. Garland, T.R. Lemberger, R. Suoryakumar, BR. Patton and R.T. Tellenhorst, High Temperature Superconductors, in: Extended Abstracts Materials Research Society Spring Meeting, 1987, p. 53. [17] K.N.R. Taylor, GJ. Russell, B. Hunter, D.N. Matthews, A. Bailey and J.I. Dunlop, J. Crystal Growth 85 (1987) 656. [181 K.N.R. Taylor, R.A. Vaile, D.N. Matthews, A. Bailey, J. Cochrane and B. Hunter, Phys. Rev. B, submitted. [19] E.M. Engler, Chem. Tech., in press. [20] R.A. Vaile, D.N. Matthews, G.J. Russell and K.N.R. Taylor, Australian Physicist 24 (1987) 87. [21] B.T. Matthias, Superconductivity of d- and f-Band Metals (New York, 1972) p. 367.
Journal of Crystal Growth 85 (1987) 628 631 North-Holland, Amsterdam
SUPERCONDUCTIVITY AT 108 K IN SULPHUR-SUBSTITUTED YEa 2Cu3O~ K.N.R. TAYLOR, D.N. MATITHEWS and G.J. RUSSELL Advanced Electronic Materials Group, School of Physics, University of New South Wales, Post Office Box 1, Kensington, NSW 2033, Australia
Received 17 September 1987; manuscript received in final form 26 September 1987
In an intensive series of investigations of the effects of elemental substitutional changes on the superconducting properties of YBa 2Cu 3O~~ we have recently studied the behaviour induced by sulphur substitution. All samples retained full superconducting transitions to 20% replacement of CuO by CuS and the 10% specimen showed a transition at 108 K. With repeated cycling, however, this degraded to 89 K at which it was stable.
1. Introduction One of the exciting features of the high temperature superconductors based qn YBa2Cu3O~ is that they are capable of extensive elemental substitution in a search for improved materials. Exhaustive studies have already been carried out by a number of research groups (see, for example, refs. [1 3]) for the case of partial or complete rare earth substitution. These have demonstrated interesting results although there has been no report of enhanced critical temperatures. Similarly, when barium is replaced with other alkaline earth metals, the overall trend is towards a continuous decrease in 7~[4]. It must be mentioned, however, that for strontium substitution, reports have recently been made of critical ternperatures close to and in excess of room temperature [5]. Copper, too, appears vital to maintaining superconducting behaviour at temperatures close to 100 K, as substitution of other transition metals has only achievedresults over ainsmall concentration range andbeen invariably eventual degradation of the resistive behaviour [6 8]. Oxygen concentration changes can be imposed by suitable thermal treatments in the range 400 600°C, and both nitrogen- and helium-induced effects are known at these temperatures [9 11]. These effects appear to be unrelated to the 0022-0248/87/$03.50 © Elsevier Science Publishers (North-Holland Physics Publishing Division)
remarkable changes which occur when either of these gases is introduced into the solid lattice at temperatures close to 77 K [12,13]. Despite these few indirect effects, however, there appears to have been little or no attempt to explore the quite extensive substitutional changes which can be made for the oxygen atoms in the various sites available in the orthorhombic perovskite structure. A number of reports using fluorine substitution suggest that these highly unstable materials may exhibit ill defined transitions to zero resistance near to 150 K [14]. One of the immediately obvious and relatively easily attained substitutions of this kind occurs through the replacement of oxygen by sulphur and in a recent series of measurements of this type we have observed a number of interesting results which are described below.
2. Results and discussion 5)~were prepared by YBa2Cu3(O, ourSamples normal of process of sintering a lightly pressed pellet of mixed compounds at 950°C for several hours followed by an extended annealing treatment at 550° during the final cool down [15]. In the present study, samples were made in which 3%, 10%, 20%, 50% and 100% of the CuO was substituted by CuS.
B.V.
K.N.R. Taylor et a!.
/ Superconductivity at 108 K in sulphur-substituted YBa2Cu3O,~
Visual inspection of the as-prepared samples for 3% and 10% substitution, after removal from the furnace, showed the presence of unusually large grains in the sample compared with those for the normal YBa 2Cu 3°x composition. The dimensions of these grains lay in the range 100—200 p~m and attempts are now being made to explore this effect as a basis for crystal growth. X-ray powder diffraction observations of the material showed that the orthorhombic phase dominated the structure for all except the 50% and 100% substituted samples. No measurable lattice parameter changes were observable (~2O 0.10) and the only significant change in the diffraction pattern was a very rapid variation of the (005) peak intensity at 38.4°, relative to either the principal (110/103) diffraction at 32.8°or the (113) peak at 40.4° as shown in fig. 1. Lee et al. [16] were the first to point out the sensitivity of this reflection to displacements of the barium atoms within the unit cell, a fact we have used to establish the nature of the structural differences between the YBa2Cu3O~ and Y2Ba3 Cu5O~compositions [17,18]. Assuming that the sulphur ions enter the lattice substitutionally at oxygen sites, then the observed dramatic changes in the intensity of the (005) reflection can occur either because of barium ion displacements towards the yttrium planes [15] or because of the increased X-ray scattering factor of sulphur compared with oxygen. Calculation of the structure factor suggests that the donunant mechanism is probably the one involving displacement of the barium ions. In view of the large crystallite growth, and the freedom from observed impurity phases in the diffraction pattern to quite large substitutional levels, we suggest that the addition of sulphur may serve to initiate and stabilize the orthorhombic lattice in these materials. Sample resistivities were measured using a conventional 4-probe configuration with a stabilized specimen current of 10 mA. Electrical contacts were made using Dolite silver paste. The specimen voltage was measured directly onto an XY recorder (Y-axis) while the thermocouple output was displayed on the X-axis which had previously been calibrated. The specimen current was monitored separately using a digital meter. All meas-
005
629
103
ito
013
106 113
________________________
40
35
31
2 e (degrees) Fig. 1. The region of the X-ray diffraction pattern containing the 005 reflection for the 3%, 10% and 20% samples showing the rapid change in relative intensity of this peak (3% at the top and 20% at the bottom).
urements were made as the temperature rose from 77 K to room temperature at a rate of 1 K/mm. The 3%, 10% and 20% samples all exhibited cornplete superconducting transitions; however, both 50% and 100% substitution of CuS for CuO resulted in semiconducting materials with room temperature resistance in excess of 106 Both the 3% and 20% samples exhibited critical temperatures close to those of the pure YBa 2Cu 3°x compound; however, the initial observational run on the 10% sample revealed a transition well in excess of 100 K, with an onset at 113.5 K and a final zero resistance (10 6 ~ cm) at 108 K, as shown in fig. 2a. Repeated cycling of all the samples, between ~,
/ Superconductivity at 108 K in sulphur-substituted YBa2Cu3O~
K.N.R. Taylor et al.
630
YBa2Cu3O~composition, at temperatures in excess of 100 K, appears to be a common feature
50 10’I
>.
I-
U)
20
~
////—IIf”~~~
1.0
a
3’!. 0
so
~o
100
110
120
130
TEMPERATURE (K)
AT
I I
E
Cycle 2 Cycle 3 CYCI~
in LU
.yclel I
1135 98 91
108 95 89
I
~ I 30 2 0
Cyc ~
C~IeI
5
-
C
___________________________________________ 80 90 100 110 120 130
~
TEMPERATURE (K)
Fig. 2. (a) The temperature variation of the resistivity in the 3%, 10% and 20% substituted samples which exhibited a superconducting transition. The final critical temperatures obtained after cycling the 3% and 20% samples are indicated. (b) The degradation of the 108 K transition with repeated cycling between 77 and 300 K. The small transients shown in the normal state of the second cycle appear to be typical of unstable materials,
room temperature and 77 K, led to a continuous degradation in their performance, as shown in fig. 2b for the 10% material with a final transition (p = 0) occurring at 89 K after three cycles. Further cycling did not lower this temperature. Parts of the sample which had remained in the laboratory atmosphere for approximately 24 h were also degraded and exhibited transition temperatures of 86 K. The stable transition temperatures of the other samples after cycling are shown in fig. 2a. Attempts to restore the high temperature superconducting state by heating (300°C for 15 mm) and vacuum treatment (2 h at room temperature) both failed to have any significant effect on the deteriorated samples. This lack of stability of superconducting transitions which occur in materials based on the
of the materials themselves. There is some evidence theseindependent transitions of arethetoprecise be found in which isthat almost details overprocessed samples [19] or compositions in the Y203—BaO—CuO phase diagram lying close to the tie-line boundaries which define the existence region of the compound [20]. Consequently, it is tempting to identify the origin of the high temperature transitions with conditions which leave the crystal structure of the material close to the limits of its stability, as was suggested by Matthias in 1971 [21] in connection with niobium based materials. Whether this is so in the present case is unclear, particularly since the evidence of both the grain sizes and X-ray diffraction data suggest that
sulphur view improve the sample rapidthe deterioration lattice in the atmosphere itmay is ofmore likely that the stability. sulphur substitutionIn leaves the vulnerable to combined water vapour and carbon dioxide attack. No sulphate formation could be detected in our sampies by X-ray diffraction or optical microscopy. Further work is in progress to establish the location of the sulphur atoms in the lattice and their effect on the carrier concentration in the samples, in order to understand the role which this atomic substitution plays in the superconducting process.
References [11 P.H. Hor, R.L. Meng, Y.Q. Wang, L. Gao, Z.J. Huang, J. Bechtold, K. Forster and C.W. Chu, Phys. Rev. Letters 58 (1987) 1891. [2] S. Hosoya, M. Onoda, S. Shamoto and M. Sato, Japan. J. Appl. Phys. 26 (1987) L456. Yamada, K. Kinoshita, A. Matsuda, T. Watanabe and Y. Asano, Japan. J. Appi. Phys. 26 (1987) L706. [4] Appi. T. Wada, Adachi, Mihara and R. Inaba, Japan. J. Phys.S. 26 (1987) T. L706. [5] H. Ihara, N. Terada, J. Jo, M. Hirabayashi. M. Tokumoto, Y. Kimura, T. Matsubara and R. Suoise, Japan. J. Appi. Phys. 26 (1987) L1413. [o] J. Tian, L.L. Wang, B.Q. Zhang, X.M. Dai, J.L. Wang and G.G. Pan, in: Proc. Beijing High 7~Superconductor Conf., June 1987.
[31T.
[7] G. Xiao, F.H. Streitz, A. Gavrin, Y.W. Du and C.L.
Chien, Phys. Rev. B35 (1987) 8782.
K.N.R. Taylor eta!.
/ Superconductivity at 108 K in sulphur-substituted
[8] S. Bosi, K.N.R. Taylor and G.J. Russell, to be published. [9] R. Beyers, G. Lim, E.M. Engler, V.Y. Lee, M.L. Ramirez, R.J. Savoy and R.D. Jacowitz, Solid State Phys., submitted. [10] Y. Ito, H. Hasegawa, K. Takagi and K. Miyanchi, Japan. J. Appl. Phys. 26 (1987) L692. [11] P.K. Gallagher, Advan. Ceram. Mater. 2 (1987) 632. [12] D.N. Matthews, A. Bailey, T. Puzzer, G.J. Russell, j Cochrane, R.A. Vaile, H.B. Sun and K.N.R. Taylor, Solid State Commun., submitted. [131 D.N. Matthews, A. Bailey, R.A. Vaile, G.J. Russell and K.N.R. Taylor, Nature 328 (1987) 786. [14] SR. Ovshinsky, R.T. Young, D.D. Allred, G. De Maggio and GA. Van der Leeden, Phys. Rev. Letters 58 (1987) 2579. [15] K.N R. Taylor, High Temperature superconductors, AEM Report 69, UNSW, 1987.
YBa
2Cu3OA
631
[16] S.J. Lee, J.P. Golben, S.Y. Lee, X.D. Chen, Y. Song, T.W. Nob, RD. McMichael, Y. Cao, J. Testa, F. Zuo, JR. Gaines, A.J. Epstein, D.L. Cox, J.C. Garland, T.R. Lemberger, R. Suoryakumar, BR. Patton and R.T. Tellenhorst, High Temperature Superconductors, in: Extended Abstracts Materials Research Society Spring Meeting, 1987, p. 53. [17] K.N.R. Taylor, GJ. Russell, B. Hunter, D.N. Matthews, A. Bailey and J.I. Dunlop, J. Crystal Growth 85 (1987) 656. [181 K.N.R. Taylor, R.A. Vaile, D.N. Matthews, A. Bailey, J. Cochrane and B. Hunter, Phys. Rev. B, submitted. [19] E.M. Engler, Chem. Tech., in press. [20] R.A. Vaile, D.N. Matthews, G.J. Russell and K.N.R. Taylor, Australian Physicist 24 (1987) 87. [21] B.T. Matthias, Superconductivity of d- and f-Band Metals (New York, 1972) p. 367.