In the Laboratory
A Simplified Synthetic Experiment of YBa2Cu3O7–x Superconductor for First-Year Chemistry Laboratory Jui-Lin She* and Ru-Shi Liu Department of Chemistry, National Taiwan University, Taipei, Taiwan, R.O.C.; *
[email protected] The YBa2Cu3O7–x (Y-123, x ≤ 0.25) high temperature superconductor shows zero resistance and the Meissner effect at superconducting temperature of ~95 K. The crystalline structure, characteristics, and applications of the Y-123 superconductor have become popular topics of modern materials science chemistry and introduced in general chemistry courses (1, 2). Synthetic experiments of Y-123 superconductors for undergraduate chemistry laboratory have been described in the literature (3–12). However, the traditional synthetic methods, such as solid-state reaction, coprecipitation reaction, and citrategel reaction included repeated grinding and heating at high temperature (ca. 930 oC) for 20–24 h. The tube furnace and oxygen supply were required in these experiments, which were difficult for the first-year students to use. In addition, the tedious preparation procedures were not easily implemented in a 3-hour chemistry laboratory course. Therefore, the objective of the current study was to demonstrate a simple method of synthesizing Y-123 superconductors that was easily adapted by first-year students and could be finished in a 3-hour laboratory class. Synthesis In a typical experiment, 0.45 g Y2O3, 1.58 g BaCO3, and 0.95 g CuO in stoichiometric quantities were weighed, mixed, and ground thoroughly in agate mortar. The fine powder of the mixture was pressed into a pellet using a die with 1 ton cm‒2 pressure. The pellet was then calcined in air at 930 oC for 10 hours
0.45 g Y2O3 (1) ground 1.58 g BaCO3 (2) pressed 0.95 g CuO –2 1 ton cm
(3) heated in air
930 pC, 10 h
atomic ratio Y:Ba:Cu = 1:2:3
YBa2Cu3O7x superconductor
Scheme I. Synthesis of Y-123 superconductor.
magnets
superconductor Figure 1. The levitation of three magnets over a Y-123 superconductor immersed in liquid nitrogen.
in a computer-controlled box furnace. The heating and cooling rate was maintained at 5 oC min‒1. After cooling to room temperature a black pellet of Y-123 superconductor having 15 mm diameter and ~3 mm thickness was obtained. The flow chart of YBa2Cu3O7–x synthesis is shown in Scheme I. Characterizations The Meissner effect was demonstrated by immersing Y-123 superconductor pellets in liquid nitrogen and placing bar magnets (NbFeB) on top of it. Hazards Both Y2O3 and BaCO3 are irritating to skin, eyes, and respiratory tract (13). BaCO3 may be fatal if swallowed (14). The processing of powders needs to be carried out in a fume hood or wearing the disposable particle mask to avoid breathing the dust. Avoid direct contact with liquid nitrogen, which can cause frostbite. Results and Discussion In this experiment, high purity starting materials, Y2O3, BaCO3, and CuO, were used directly without further treatment. The reduced quantity of chemicals costs less than one U.S. dollar per pellet and can be adjusted according to the diameter of the dies. Both the stoichiometric atomic ratio of Y:Ba:Cu (1:2:3), and the homogeneity of ground powder were important to ensure high purity and successful synthesis of the superconductor. Controlling the pressure used in disc formation to under 1 ton cm‒2 was also noteworthy, as the greater pressure may cause cracking of the pellet after heating because of the evolution of CO2 gas. The equipment used in processing, such as agate mortar, hydraulic press, and dies were commonly available in most chemistry laboratories. The pellet was calcined in air at 930 oC for 10 hours in a computer-controlled box furnace (internal dimensions: 30 × 30 × 30 cm). One could accommodate 16–20 specimens heated at one time and avoid using tube furnace as well as oxygen supply, which were difficult to operate in a first-year chemistry laboratory. The synthetic procedures could be finished by a class of 20 groups of students in 3-h laboratory session. The heating process was controlled by a computer program that ran overnight. In the following week, students immersed the products in liquid nitrogen and observed the levitation of magnets to test the Meissner effect. The majority of student groups (about 99%) succeeded in making Y-123 discs that showed the Meissner effect at liquid nitrogen temperature (Figure 1). Most of the synthesized Y-123 superconductors (~76%) levitated one magnet to a 4 mm height and ~23% of the samples levitated one magnet to a 2 mm height.
© Division of Chemical Education • www.JCE.DivCHED.org • Vol. 85 No. 6 June 2008 • Journal of Chemical Education
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30
40
60
( 205)
( 018) ( 117) ( 026)
( 025)
( 213)
( 116) 50
2 R / deg
( 115) ( 016) ( 023) ( 007) ( 122)
( 006) ( 020)
( 112)
( 200)
( 005) ( 014) ( 104) ( 113)
YBa2Cu3O7x space group: Pmmm crystal system: orthorhombic lattice constants: a = 3.82 Å, b = 3.89 Å, c = 11.67 Å
( 013) 20
( 012) ( 102)
(003)
Intensity
Some of the superconductors could levitate 3–6 bar magnets at the same time. Besides the exhibition of the Meissner effect, the X-ray powder diffraction (XRD) pattern of the prepared products also showed orthorhombic phase with high purity (Figure 2). The height of levitation depended on the homogeneity and purity of the sample. To analyze the phase purity of the superconductor, the experimental XRD could be further designed and served as an extension in advanced laboratory course. According to the survey questionnaires completed at the end of the lab, students were interested in this experiment. They could synthesize the superconductors, obtain the products, and test the Meissner effect by themselves. It was exciting to use the equipment that was seldom used in first-year chemistry laboratory, such as agate mortar and hydraulic press. It was also fun to handle liquid nitrogen with the proper precautions. The experiment motivated many of the students to learn more about the concepts of superconductivity, superconducting transition temperature, and solid-state reaction.
( 103) ( 110)
In the Laboratory
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Figure 2. X-ray powder diffraction pattern of Y-123 superconductor prepared from the chemistry laboratory.
Conclusions The study provides a simplified synthetic experiment of YBa2Cu3O7–x superconductor. It takes less heating time, consumes less energy, and decreases the cost for chemicals that meets the requirements of green chemistry. The experiment is easily performed and successfully applied to a 3-hour firstyear chemistry laboratory class. By using this simple protocol, students can synthesize their own superconductors and test the Meissner effect in the laboratory directly without much effort. Accordingly, students found the concept of superconductivity interesting; learned the skills of grinding, pressing, and calcinations, which are used in solid-state reactions; and gained insight into materials science chemistry. Acknowledgments We thank the teaching assistants for their help in collecting the students’ data. The financial support from the Ministry of Education, Taiwan, R.O.C. is gratefully acknowledged. Literature Cited 1. Zumdahl, S. S. Chemical Principles, 5th ed.; Houghton Mifflin Co.: Boston, 2005; pp 788–789. 2. Brown, T. L.; LeMay, H. E., Jr.; Bursten, B. E. Chemistry, the Central Science, 10th ed.; Pearson, Prentice Hall: Upper Saddle River, NJ, 2006; pp 491–494. 3. Harris, D. C.; Hills, M. E.; Hewston, T. A. J. Chem. Educ. 1987, 64, 847–850. 4. Juergens, F. H.; Ellis, A. B.; Dieckmann, G. H.; Perkins, R. I. J. Chem. Educ. 1987, 64, 851–853.
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5. Jacob, A. T.; Pechmann, C. I.; Ellis, A. B. J. Chem. Educ. 1988, 65, 1094–1095. 6. Djurovich, P. I.; Watts, R. J. J. Chem. Educ. 1993, 70, 497–498. 7. Cogdell, C. D.; Wayment, D. G.; Casadonte, D. J., Jr.; KubatMartin, K. A. J. Chem. Educ. 1995, 72, 840–841. 8. Roesky, H. W.; Möckel, K. Chemical Curiosities: Spectacular Experiments and Inspired Quotes; VCH: New York, 1996; pp 240–242. 9. Fahlman, B. D. J. Chem. Educ. 2001, 78, 1182. 10. Hoppé, J. I.; Malati, M. A. J. Chem. Educ. 2005, 82, 299–301. 11. University of Wisconsin. http://www.mrsec.wisc.edu/Edetc/nanolab/YBaCuO/index.html (accessed Feb 2008). 12. She, J. L.; Liu, R. S. Chemistry (The Chinese Chem. Soc., Taipei), 1999, 57, 143-148. 13. The Merck Index, 11th ed.; Budavari, S., Ed.; Merck and Co.: Rahway, NJ, 1989. 14. Barium Carbonate MSDS. http://www.jtbaker.com/msds/englishhtml/B0348.htm (accessed Feb 2008).
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Journal of Chemical Education • Vol. 85 No. 6 June 2008 • www.JCE.DivCHED.org • © Division of Chemical Education
