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Environmental reactivity characteristics of K3C60 and YBa2Cu3O7−x high-temperature superconductor thin films
0038-1098/93$6.00+.00 Pergamon Press Ltd
Solid State Communications, Vol. 88, No. 6, pp. 43 l-434, 1993 Printed in Great Britain.
ENVIRONMENTAL REACTIVITY CHARACTERISTICS OF K3Q-J AND HIGH-TEMPERATURE SUPERCONDUCTOR THIN FILMS
Y!hl2ClJ307.x
David R. Riley, David Jurbergs, Ji-Ping Zhou, Jianai Zhao, and John T. McDevitt* Department of Chemistry and Biochemistry, The University of Texas at Austin Austin, Texas 78712-1167 (Received 3 August 1993,accepted 7 September 1993 by A. H. MacDonald) Recently the environmental reactivity behavior of the copper-oxide superconductors has been studied and the following reactivity trends have been established: YBaZCu307
>
h.&ro.1sQQ
Tl2Ba2Ca2Cu3019 7
Ndi.85Ceo.dU04
7
Bi2Sr2CaCu208 7
Z
NdmTho.15CUQ
In this paper, the degradation characteristics of the most reactive cuprate material, YBazCu307, are compared with those of the fulleride superconductor, K3C6n. Conductivity vs. exposure time measurements acquired for thin film samples in eight different environments are utilized to estimate the degradation rates for the two superconductor materials. The cuprate superconductor remains relatively stable in the presence of dry nitrogen, dry oxygen, vacuum, air and acetonittile environments, but degrades rapidly upon exposure to water solutions. Samples of K3C69 are also unreactive in dry nitrogen and under vacuum, but decompose extremely rapidly upon exposure to dry oxygen, air, acetonitrile or water solutions resulting in the complete loss of the
Although the initial gas phase studies completed with C& su gested-that the full&ne compounds are-extreme1 stable.$l2 more recent solution uhase exneriments 13-2$ have shown that the Q-J molecule’displaysrich chemistry. Consequently, a number of strategies have been develo to chemically derivatize the parent molecule.l2vl5*l f?ed .23 Moreover, gas phase studies of 0 and C70 anions have shown that these materials react with reagents such as BF3 and NO2.l l It has been known also for some time that alkali metal-doped C6O compounds are not generally air stable.9-l0,24,25 However. to our knowledge! no systematic study directed at quantifying the reactrvrty characteristics of the doped fulleride superconductors has been completed. Here we compare the thin film reactivity behavior of K3Q3 with that of YBa2Cu3@ in eight different environments. Prior to the reactivity measurements, samples of C were synthesized and purified as reported elsewhere. 58 9 Thin films of K3C6o were prepared by subliming the fullerene material onto glass substrates (5 x lo-6 torr at SWC) and then doping the specimens with potassium metal vapor (5 x lo-6 torr at 1250C). Initial experiments used glass substrates with platinum sputtered onto the comers to ensure intimate contact between the C6O film and the electrical connections. Subsequent experiments were completed with copper leads directly connected to the C6O samples. Both techniques yielded similar results and provided reliable measurements. Using a rocedure analogous to that reported by Haddon et al., 7 29 the formation of stoichiometric K3C6o was inferred by monitoring the film resistivity during the doping process with termination of the metal vapor treatment upon reaching the minimum resistivity value (- 2 x IO-3 Q-cm). Thin films
The discoveries of superconductivit in the cuprate compounds1-2 and doped fullerene phases r have caused a tremendous amount of research activity to be directed towards the study of these remarkable materials. The cuprate materials have extended the upper limit of stable, reproducible superconductivity to temperatures near 130 K. Moreover, processing methods have now been established whereby YBa2Cu307_x films can be prepared exhibitin critical current densities of -107 A/cm2 at 77 K. $ Meanwhile, the discovery of the fullerene based systems has catalyzed a large amount of effort to be directed towards the study of the structural, physical and chemical properties Metal doped C60 of these new carbon allotropes. compounds5 such as K3C60, Cs3C60, and Rb2CsC6t-rhave been shown to exhibit superconductivity with transition temperatures as high as 33 K. In order to foster more rapid developments in the area of high-Tc research, a more complete understanding of the environmental reactivity characteristics of these superconductors is required now. The cuprate phases degrade rapidly when in the presence of water, acids, carbon dioxide or carbon monoxide.6 Using techniques such as X-ray powder diffraction (XRD), scanning-electron microscopy (SEM), electrochemistry, X-ray photoelectron spectroscopy (XPS), Auger spectroscopy, energy-dispersive spectroscopy (IDS) and conductivity measurements, a comprehensive comparison of the reactivit with water of the common highTc phases was completed -r-8 recently with the establishment of the following relative reactivity scale: YBa2cu307
Bi2Sr2CaCu20g %35Ce0.15Cu04
7
T12B%!~cu3010
2
La1.85sr0.15cuo4 >
' '
Ndl.85n0.15cuo4 471
432
ENVIRONMENTAL REACTIVITY CHARACTERISTICS
Vol. 88, N&6
C
1
2
Time / (hours)
Time / (hours)
Figure 1. Log sample resistivity vs. exposure time for three YBa2Cu307-x thin films that were exposed to (A) dry nitrogen, (B) air (with ambient humidity), and (C) water vapor equilibrated at 25OC. All sample resistivity values are normalized to the initial value (- 100 m W-cm). Films were deposited by the laser ablation method and all the specimens displayed thickness values close to SOOOA. A(O), B(0) and C(0) represent the exact time that the films were exposed to nitrogen, air and water vapor, respectively. Prior to exposure, baseline resistivity values for the samples were acquired in vacuum at 10-6 torr.
Figure 2. Log sample resistivity vs. exposure time for three K3C60 films that were exposed to (A) dty nitrogen, (B) air (with ambient humidity), and (C) witer viper eauilibrated at 25OC. All samule resistivitv values are n&malized to the initial value fo; the pristine’film (i 2000 m W-cm). All films were - MOOAin thickness. A(O), B(0) and C(0) represent the exact time that the films were exposed to nitrogen, air and water vapor, respectively. prior to exposure, baseline resistivity values for the samples were acquired in vacuum at 10m6torr.
of YBa2Cu307 were prepared using the laser ablation method.30 Both the YBazCu307 and K3C60 films were prepared as continuous thin films with smooth morphologies having thickness values close to 30ooA. X-ray powder diffraction, four-point probe, magnetic susceptibility and scanning electron microscopy measurements were used to characterize the materials; unit cell dimensions and transition temperature values agreed closely with those previously reported.30-31 Nearly 100% dense films of both C60 and
YBa2Cu307 acquired with grain sizes of 0.3 - 0.5 pm for both materials. Because of the highly reactive nature associated with the doped fulleride materials, conventional methods of exploring the degradation rates of these compounds could not be applied. Rather, here we monitor the conductivity of the films as a function of exposure time to various environments as a means to estimate the reactivity characteristics of the samples. Thus, after depositing the
I. Demadation Rates for K-L&J and YBa2&3Q7 m K3C60 Environment *2
YBa2Cu307 cm / hour)
40
a -_-__
Vacuum
a _--_-
Dry O2
3x lo6
0.8 4
Air CH3CN
1 x loa 4 x 108
7 10
H20 Vapor
3x 102
5%H20 / 95%CH3CN
4 x 1010 b ______
100% H20
b -_____
a
1 x 102 4 x 103
Very slight decreases in the resistance of these samples were noted. b Samples immediately dissolved in these environments and no degradation rates could be determined.
Vol. 88, No. 6
ENVIRONMENTAL REACTIVITY CHARACTERISTICS
films, the specimens were transferred to an inert atmosphere glove box, loaded into a chamber that was equi ped with electrical fee&roughs and then evacuated to IO-t? torr. The reactivity characteristics of the films were determined by monitoring their resistivity values as a function of exposure time to various environments. As the specimens degraded, the resistivity of the film increased due to the formation of nonconducting degradation products. Measurement of the initial rate of increase in the film resistivity was used to quantify the degradation rates for the films upon exposure to the respective environments. Figure 1 illustrates the time evolution of the resistivity values acquired for YBa2Cu307 thin films that were exposed to nitrogen, air and water vapor. In the nitrogen atmosphere (Figure IA), YBazCu307 is quite stable as it displays no appreciable resistivity increase even after months of exposure. A very small, but continuous increase in the tesistivity is observed when the film is exposed to air (Figure IB). More rapid degradation is noted when YBazCu307 is exposed to water vapor equilibrated at 250C (Fieure 10 Here a rauid initial rise in film resistivitv is no&, followed by a n&e gradual increase. The initial rapid rise in resistivity is likely due to degradation which occurs selectively along the grain boundaries32 and the subsequent gradual increase is probably a result of decomposition which occurs within the individual grains. Thus, the YBa2Cu307 films are stable in dry nitrogen and vacuum environments; are slightly reactive in air and acetonitrile environments; and ate highly reactive in water solutions (Table I). Similar measurements completed for K3Q films are
433
illustrated in Figure 2. Accordingly, in nitrogen the K3Ceu films are relatively stable as they display very little changes in resistivity (Figure 2A). However; upon exposure-to either air (Fieure 2B) or water vanor (Fiaure 2C). the K3CN) - :films degrade extremely rapidly, -at-which .time. their resistivity values increase past the instrumentation limits. As summarized in Table I. the K3C613films are relatively stable in dry nitrogen and under vacuum but decompose rapidly in the presence of dry oxygen, air, acetonitrile and water vapor. Interestingly, water vapor degrades K3Ca much more rapidly than does oxygen gas. In summary, both YBazCu307 and K3C6o superconductors degrade when in the presence of many atmospheric components. It has been shown here that the most reactive cuprate material, YBa2Cu307, is far more stable than the fulleride-based material, K3Ca. In many reactive environments, the K3Cm superconductor degrades up to eight orders of magnitude faster than does YBaTCu307. Thus. uractical utilization of fulleride supe
References
J.G. Bednorz. K.A. Mtiller Z. Phys. B. 1986.64. 189. 2. C.W. Chu, T.H. Hor. R.L. Meng, G. Gao, Z.J. Huana. Y.Q. Wang Phvs. Rev. B 1987.35.405. 3. A.F. Hebar& M.J: Rosseinsky, R.C. Haddon. D.W. Murphy, S.H. Glarum, T.T.M. Palstra. A.P. Ramirez. A.R. Kortan Nature 1991.350,600. 4. R. McConnell, S. Wolf (ed.) Science of, Plenum, New York, 1989. 5. K. Tanigaki, T.W. Ebbesen, S. Saito, J. Mizuki, J.S. Tsai. Y. Kubo. S. Kuroshima Nature 1991.352.222. 6. J.T. .McDevitt, D.R. Riley, S.G. Haupt &za&tical Chemistry l993,65,535A. 7. D.R. Riley, J.P. Zhou, A. Manthiram, J.T. McDevitt . . . in tiered . -on. w . and MRS Symposium Series, Edited by Shaw, D.T.; Tsuki. C.C.; Schneider, T.R.; Shiohara. Y.. 1992, 275, 711. 8. J.P. Zhou. D.R. Riley, A. Manthiram, M. Arnedt. R. Schmerling. J.T. McDevitt Appl. Phys. Len. accepted. 9. H.W. Kroto, J.R. Heath, S.C. O’Brien, R.F. Curl, R.E. Smalley Narure 1985,318, 162. 10. Q.L. Zhang, S.C. O’Brien, J.R. Heath, Y. Liu, R.F. Curl, H.W. Kroto, R.E. Smalley J. Phys. Chem. 1986.90, 525. 11. L.S. Sunderlin, J.S. Paulino, J. Cow, B. Kahr. D. Ben-Amotz, R.R. Squires J. Am. Chem. Sot. 1991. 113,5489. 12. H.W. Kroto. A.W. Allaf, S.P. Balm Chem. Rev. 1.
1991.91.
1213.
13. R. Taylor, J.P. Parsons. A.G. Avent, S.P. Rannard, TJ. Dennis, J.P. Hare, H.W. Kroto. D.R.M. Walton Nature 1991,351, 277. 14. D. Heymann Carbon 1991,29.684.
15. J.M. Hawkins, T.A. Lewis, S.D. Loren. A. Meyer, J.R. Heath, Y. Shibato. R.J. Saykally J. -Org. &em. 1990.55.
6250.
16. R.E. Haufler, J. Conceicao, L.P.F. Chibante, Y. Chai, N.E. Byrne, S. Flanagan, M.M. Haley, S.C. O’Brien, C.P. Xiao. W.E. Billups. M.A. Ciufolini, R.H. Hauge, J.L. Margrave, L.J. Wilson, R.F. Curl, R.E. Smalley J. Phys.Chem. 1990,94. 8634. 17. F. Zhou, S.L. Yau. C. Jehoulet. D.A. Laude, Z. Guan, A.J. Bard J. Phys. Chem. 1992.96, 4160. 18. C. Jehoulet. Y.S. Obeng, Y.T. Kim, F. Zhou. A.J. Bard J. Am. Chem. Sot. 1992.114.4237. 19. C. Jehoulet. A.J. Bard J. Am. Chem. Sot. 1991,113, 5456. 20. D. Dubois, K.M. Kadish, S. Flanagan, L.J. Wilson J. Am. Chem. Sot. 1991,113, 7773. 21. P.M. Allemand, A. Koch, F. Wudl, Y. Rubin, F. Diederich, M.M. Alvarez, S.J. Anz, R.L. Whetten J. Am. Chem. Sot. 1991,113, 1050. 22. B. Miller, J.M. Rosamilia. D. Dabbagh, R. Tyoko, R.C. Haddon, A.J. Muller, W. Wilson, D.W. Murphy, A.F. Hebard J. Am. Chem. Sot. 1991,113, 6291. 23. R.F. Curl. R.E. Smalley Scienrific American 1991, 265, 54. . . and of Fu 24. A.F. Hebard in avsics Systems: NATO, AS1 Series (Eds. P. Jena, S.N. Khanna, and B.K. Rao; Kluwer Academic Publishers, Dordrecht 1992). 25. K. Holczer, 0. Klein, S.M. Huang. R.B. Kaner, K.J. Fu, R.L. Whetten, F. Diederich Science 1991.252, 1154. 26. N. Kratschmer, L.D. Lamb, K. Fostiropoulos. D.R. Huffman Nature 1990, 347. 354. 27. R.C. Haddon, A.F. Hebard, M.J. Rosseinsky. D.W. Murphy, S.H. Glarum, T.T.M. Palstra, A.P. Ram&z,
434
ENVIRONMENTAL REACTIVITY CHARACTERISTICS
S.J. Duclos, R.M. Fleming, T. Siegrist, R. Tycko in mSvnthesis. ACS Symposium Series 1992,481,7 1. 28. R.C. Haddon, A.F. Hebard, M.J. Rosseinsky, D.W. Murphy, S.J. Duclos, K.B. Lyons, B. Miller, J.M. Rosamilia, R.M. Fleming, A.R. Kortan, S.H. Glarum, A.V. Makhija, A.J. Muller, R.H. Eick. S.M. Zahurak, R. Tycko, G. Dabbagh, F.A.Thiel Narure 1991,350, 320. 29. G.P. Kochanski, A.F. Hebard, R.C. Haddon, A.T. Fiory Science 1992,255, 184. 30. D. Dijkkamp Appl. Phys. L-a_%.1987,51, 619.
Vol. 88, No: 6
31. R.M. Fleming, A.P. Ramirez, M.J. Rosseinsky, D.W. Murphy, R.C. Haddon, S.M. Zahurak, A.V. Makhija Nature 1991,352,787. 32. J.P. Zhou, D.R. Riley, J.T. McDevitt Chem. Marer. 1993,5, 361. 33. J.R. Heath. S.C. O’Brien. Q. Zhang, Y. Liu, R.F. Curl, H.W. Kroto, F.K. Tittel, R.E. Smalley J. Am. Chem. Sot. 1985,107, 7779. 34. Y. Chai, T. Guo, C. Jin, R.E. Haufler, L.P.F. Chibante, J. Fore, L. Wang, J.M. Alford. R.E. Smalley J. Phys. Chem. 1991,95, 7564.
Solid State Communications, Vol. 88, No. 6, pp. 43 l-434, 1993 Printed in Great Britain.
ENVIRONMENTAL REACTIVITY CHARACTERISTICS OF K3Q-J AND HIGH-TEMPERATURE SUPERCONDUCTOR THIN FILMS
Y!hl2ClJ307.x
David R. Riley, David Jurbergs, Ji-Ping Zhou, Jianai Zhao, and John T. McDevitt* Department of Chemistry and Biochemistry, The University of Texas at Austin Austin, Texas 78712-1167 (Received 3 August 1993,accepted 7 September 1993 by A. H. MacDonald) Recently the environmental reactivity behavior of the copper-oxide superconductors has been studied and the following reactivity trends have been established: YBaZCu307
>
h.&ro.1sQQ
Tl2Ba2Ca2Cu3019 7
Ndi.85Ceo.dU04
7
Bi2Sr2CaCu208 7
Z
NdmTho.15CUQ
In this paper, the degradation characteristics of the most reactive cuprate material, YBazCu307, are compared with those of the fulleride superconductor, K3C6n. Conductivity vs. exposure time measurements acquired for thin film samples in eight different environments are utilized to estimate the degradation rates for the two superconductor materials. The cuprate superconductor remains relatively stable in the presence of dry nitrogen, dry oxygen, vacuum, air and acetonittile environments, but degrades rapidly upon exposure to water solutions. Samples of K3C69 are also unreactive in dry nitrogen and under vacuum, but decompose extremely rapidly upon exposure to dry oxygen, air, acetonitrile or water solutions resulting in the complete loss of the
Although the initial gas phase studies completed with C& su gested-that the full&ne compounds are-extreme1 stable.$l2 more recent solution uhase exneriments 13-2$ have shown that the Q-J molecule’displaysrich chemistry. Consequently, a number of strategies have been develo to chemically derivatize the parent molecule.l2vl5*l f?ed .23 Moreover, gas phase studies of 0 and C70 anions have shown that these materials react with reagents such as BF3 and NO2.l l It has been known also for some time that alkali metal-doped C6O compounds are not generally air stable.9-l0,24,25 However. to our knowledge! no systematic study directed at quantifying the reactrvrty characteristics of the doped fulleride superconductors has been completed. Here we compare the thin film reactivity behavior of K3Q3 with that of YBa2Cu3@ in eight different environments. Prior to the reactivity measurements, samples of C were synthesized and purified as reported elsewhere. 58 9 Thin films of K3C6o were prepared by subliming the fullerene material onto glass substrates (5 x lo-6 torr at SWC) and then doping the specimens with potassium metal vapor (5 x lo-6 torr at 1250C). Initial experiments used glass substrates with platinum sputtered onto the comers to ensure intimate contact between the C6O film and the electrical connections. Subsequent experiments were completed with copper leads directly connected to the C6O samples. Both techniques yielded similar results and provided reliable measurements. Using a rocedure analogous to that reported by Haddon et al., 7 29 the formation of stoichiometric K3C6o was inferred by monitoring the film resistivity during the doping process with termination of the metal vapor treatment upon reaching the minimum resistivity value (- 2 x IO-3 Q-cm). Thin films
The discoveries of superconductivit in the cuprate compounds1-2 and doped fullerene phases r have caused a tremendous amount of research activity to be directed towards the study of these remarkable materials. The cuprate materials have extended the upper limit of stable, reproducible superconductivity to temperatures near 130 K. Moreover, processing methods have now been established whereby YBa2Cu307_x films can be prepared exhibitin critical current densities of -107 A/cm2 at 77 K. $ Meanwhile, the discovery of the fullerene based systems has catalyzed a large amount of effort to be directed towards the study of the structural, physical and chemical properties Metal doped C60 of these new carbon allotropes. compounds5 such as K3C60, Cs3C60, and Rb2CsC6t-rhave been shown to exhibit superconductivity with transition temperatures as high as 33 K. In order to foster more rapid developments in the area of high-Tc research, a more complete understanding of the environmental reactivity characteristics of these superconductors is required now. The cuprate phases degrade rapidly when in the presence of water, acids, carbon dioxide or carbon monoxide.6 Using techniques such as X-ray powder diffraction (XRD), scanning-electron microscopy (SEM), electrochemistry, X-ray photoelectron spectroscopy (XPS), Auger spectroscopy, energy-dispersive spectroscopy (IDS) and conductivity measurements, a comprehensive comparison of the reactivit with water of the common highTc phases was completed -r-8 recently with the establishment of the following relative reactivity scale: YBa2cu307
Bi2Sr2CaCu20g %35Ce0.15Cu04
7
T12B%!~cu3010
2
La1.85sr0.15cuo4 >
' '
Ndl.85n0.15cuo4 471
432
ENVIRONMENTAL REACTIVITY CHARACTERISTICS
Vol. 88, N&6
C
1
2
Time / (hours)
Time / (hours)
Figure 1. Log sample resistivity vs. exposure time for three YBa2Cu307-x thin films that were exposed to (A) dry nitrogen, (B) air (with ambient humidity), and (C) water vapor equilibrated at 25OC. All sample resistivity values are normalized to the initial value (- 100 m W-cm). Films were deposited by the laser ablation method and all the specimens displayed thickness values close to SOOOA. A(O), B(0) and C(0) represent the exact time that the films were exposed to nitrogen, air and water vapor, respectively. Prior to exposure, baseline resistivity values for the samples were acquired in vacuum at 10-6 torr.
Figure 2. Log sample resistivity vs. exposure time for three K3C60 films that were exposed to (A) dty nitrogen, (B) air (with ambient humidity), and (C) witer viper eauilibrated at 25OC. All samule resistivitv values are n&malized to the initial value fo; the pristine’film (i 2000 m W-cm). All films were - MOOAin thickness. A(O), B(0) and C(0) represent the exact time that the films were exposed to nitrogen, air and water vapor, respectively. prior to exposure, baseline resistivity values for the samples were acquired in vacuum at 10m6torr.
of YBa2Cu307 were prepared using the laser ablation method.30 Both the YBazCu307 and K3C60 films were prepared as continuous thin films with smooth morphologies having thickness values close to 30ooA. X-ray powder diffraction, four-point probe, magnetic susceptibility and scanning electron microscopy measurements were used to characterize the materials; unit cell dimensions and transition temperature values agreed closely with those previously reported.30-31 Nearly 100% dense films of both C60 and
YBa2Cu307 acquired with grain sizes of 0.3 - 0.5 pm for both materials. Because of the highly reactive nature associated with the doped fulleride materials, conventional methods of exploring the degradation rates of these compounds could not be applied. Rather, here we monitor the conductivity of the films as a function of exposure time to various environments as a means to estimate the reactivity characteristics of the samples. Thus, after depositing the
I. Demadation Rates for K-L&J and YBa2&3Q7 m K3C60 Environment *2
YBa2Cu307 cm / hour)
40
a -_-__
Vacuum
a _--_-
Dry O2
3x lo6
0.8 4
Air CH3CN
1 x loa 4 x 108
7 10
H20 Vapor
3x 102
5%H20 / 95%CH3CN
4 x 1010 b ______
100% H20
b -_____
a
1 x 102 4 x 103
Very slight decreases in the resistance of these samples were noted. b Samples immediately dissolved in these environments and no degradation rates could be determined.
Vol. 88, No. 6
ENVIRONMENTAL REACTIVITY CHARACTERISTICS
films, the specimens were transferred to an inert atmosphere glove box, loaded into a chamber that was equi ped with electrical fee&roughs and then evacuated to IO-t? torr. The reactivity characteristics of the films were determined by monitoring their resistivity values as a function of exposure time to various environments. As the specimens degraded, the resistivity of the film increased due to the formation of nonconducting degradation products. Measurement of the initial rate of increase in the film resistivity was used to quantify the degradation rates for the films upon exposure to the respective environments. Figure 1 illustrates the time evolution of the resistivity values acquired for YBa2Cu307 thin films that were exposed to nitrogen, air and water vapor. In the nitrogen atmosphere (Figure IA), YBazCu307 is quite stable as it displays no appreciable resistivity increase even after months of exposure. A very small, but continuous increase in the tesistivity is observed when the film is exposed to air (Figure IB). More rapid degradation is noted when YBazCu307 is exposed to water vapor equilibrated at 250C (Fieure 10 Here a rauid initial rise in film resistivitv is no&, followed by a n&e gradual increase. The initial rapid rise in resistivity is likely due to degradation which occurs selectively along the grain boundaries32 and the subsequent gradual increase is probably a result of decomposition which occurs within the individual grains. Thus, the YBa2Cu307 films are stable in dry nitrogen and vacuum environments; are slightly reactive in air and acetonitrile environments; and ate highly reactive in water solutions (Table I). Similar measurements completed for K3Q films are
433
illustrated in Figure 2. Accordingly, in nitrogen the K3Ceu films are relatively stable as they display very little changes in resistivity (Figure 2A). However; upon exposure-to either air (Fieure 2B) or water vanor (Fiaure 2C). the K3CN) - :films degrade extremely rapidly, -at-which .time. their resistivity values increase past the instrumentation limits. As summarized in Table I. the K3C613films are relatively stable in dry nitrogen and under vacuum but decompose rapidly in the presence of dry oxygen, air, acetonitrile and water vapor. Interestingly, water vapor degrades K3Ca much more rapidly than does oxygen gas. In summary, both YBazCu307 and K3C6o superconductors degrade when in the presence of many atmospheric components. It has been shown here that the most reactive cuprate material, YBa2Cu307, is far more stable than the fulleride-based material, K3Ca. In many reactive environments, the K3Cm superconductor degrades up to eight orders of magnitude faster than does YBaTCu307. Thus. uractical utilization of fulleride supe
References
J.G. Bednorz. K.A. Mtiller Z. Phys. B. 1986.64. 189. 2. C.W. Chu, T.H. Hor. R.L. Meng, G. Gao, Z.J. Huana. Y.Q. Wang Phvs. Rev. B 1987.35.405. 3. A.F. Hebar& M.J: Rosseinsky, R.C. Haddon. D.W. Murphy, S.H. Glarum, T.T.M. Palstra. A.P. Ramirez. A.R. Kortan Nature 1991.350,600. 4. R. McConnell, S. Wolf (ed.) Science of, Plenum, New York, 1989. 5. K. Tanigaki, T.W. Ebbesen, S. Saito, J. Mizuki, J.S. Tsai. Y. Kubo. S. Kuroshima Nature 1991.352.222. 6. J.T. .McDevitt, D.R. Riley, S.G. Haupt &za&tical Chemistry l993,65,535A. 7. D.R. Riley, J.P. Zhou, A. Manthiram, J.T. McDevitt . . . in tiered . -on. w . and MRS Symposium Series, Edited by Shaw, D.T.; Tsuki. C.C.; Schneider, T.R.; Shiohara. Y.. 1992, 275, 711. 8. J.P. Zhou. D.R. Riley, A. Manthiram, M. Arnedt. R. Schmerling. J.T. McDevitt Appl. Phys. Len. accepted. 9. H.W. Kroto, J.R. Heath, S.C. O’Brien, R.F. Curl, R.E. Smalley Narure 1985,318, 162. 10. Q.L. Zhang, S.C. O’Brien, J.R. Heath, Y. Liu, R.F. Curl, H.W. Kroto, R.E. Smalley J. Phys. Chem. 1986.90, 525. 11. L.S. Sunderlin, J.S. Paulino, J. Cow, B. Kahr. D. Ben-Amotz, R.R. Squires J. Am. Chem. Sot. 1991. 113,5489. 12. H.W. Kroto. A.W. Allaf, S.P. Balm Chem. Rev. 1.
1991.91.
1213.
13. R. Taylor, J.P. Parsons. A.G. Avent, S.P. Rannard, TJ. Dennis, J.P. Hare, H.W. Kroto. D.R.M. Walton Nature 1991,351, 277. 14. D. Heymann Carbon 1991,29.684.
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