Pressure Dependence of Crystal Growth in a Bi-Pb-Sr-Ca-Cu-O Superconductor Prepared by Shock Compression
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Pressure Dependence of Crystal Growth in a Bi-Pb-Sr-Ca-Cu-O Superconductor Prepared by Shock Compression Takaki Kameya1, Shigeya Tomioka1, Hiroshi Kezuka1, Makoto Tsuruoka1, Shunichi Arisawa2, Tamio Endo3, Kazuhiro Endo4, Liliang Chen5 and Tsutomu Mashimo5 1 Tokyo University of Technology, 1404-1 Katakura-machi, Hachioji, Tokyo 192-0982, Japan 2 National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan 3 Mie University, 1577 Kurimamachiya-cho, Tsu, Mie 514-8507, Japan 4 Kanazawa Institute of Technology, 7-1 Ohgigaoka, Nonoichi, Ishikawa 921-8501, Japan 5 Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan ABSTRACT In this paper, the effect of shock compression on the synthesis of a Bi-based oxide superconductor was investigated. Bi1.85-Pb0.35-Sr1.90-Ca2.05-Cu3.05-Ox calcined powder was shockcompacted around 20 GPa and 30 GPa, and divided specimens were annealed at 845 ˚C for 1, 6 and 48 hours. The specimens were evaluated by x-ray diffraction and scanning electron microscope. INTRODUCTION High-pressure phase transition sometimes changes the character of materials and new superconducting phases [1-3]. Bi-Pb-Sr-Ca-Cu-O superconductors are fabricated by the shock compression method in order to establish a technique for higher-quality synthesis—larger crystal grains, predominance of the (BiPb)2Sr2Ca2Cu3Ox (Bi-2223) phase and better Tc—Bi-based oxide superconductors. Conventionally, shock-compacted Bi-based oxide superconductors are prepared under shock pressure of around 10 GPa [5-7]. In this research, starting materials were shock-compacted around 20 GPa and 30 GPa to reveal pressure dependence. After the shock compaction process, specimens were annealed, and evaluated by x-ray diffraction (XRD) and scanning electron microscope (SEM). EXPERIMENT Shock-compaction process Bi1.85-Pb0.35-Sr1.90-Ca2.05-Cu3.05-Ox calcined powder was used as a starting material. The average diameter of the starting material was 22.3 μm. The starting material was tightly encased in two steel capsules. Shock compression experiments were carried out under shock pressure of 31.42 GPa for capsule No. 1 and 21.48 GPa for capsule No. 2 at Kumamoto University, Japan. Table I shows details of the shock compression experiment. Table I. Shock compression experiment. No. 1 2
Material of projectile W Cu
Speed of projectile (km/s) 1.068 1.019
Pressure (GPa) 31.42 21.48
Annealing process Each shock-compacted Bi-Pb-Sr-Ca-Cu-O bulk was divided into four groups. The divided specimens were annealed at 845 ˚C in an air atmosphere for 1, 6 and 48 h in an electric furnace. DISCUSSION XRD analysis Figure 1 shows the XRD pattern of specimens. The peaks of (BiPb)2Sr2Ca2Cu3Ox (Bi2223) phase were indexed by using ICDD JCPDS No. 81-1541 and the peaks of (BiPb)2Sr2CaCu2Ox (Bi-2212) phase were indexed by ICDD JCPDS No. 80-2030. In both annealed specimens, more peaks of the Bi-2223 phase and Bi-2212 phase were found, and intensity of Bi-2223 phase became relatively higher in comparison with Bi-2212 phase. Usually, however, mor
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