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| 題 名 | High-Pressure Synthesis and Characterization of Some Ca-Doped R₂Ba₄Cu₇O₁₅-δ (R=Y,Sm,Dy) Cuprate Superconductors |
|---|---|
| 作 者 | Chen,Teng-ming; Yarng,S. L.; Lin,J. P.; | 書刊名 | Chinese Journal of Physics |
| 卷 期 | 36:2(Part2) 民87.04 |
| 頁 次 | 頁371-377 |
| 分類號 | 337.473 |
| 關鍵詞 | 超導體; |
| 語 文 | 英文(English) |
| 英文摘要 | Three series of (R₁-xCax)₂Ba₄Cu₇O₁₅-δ(Ca-doped R247; R = Y, Sm, Dy) cuprate superconductors have been synthesized at 990° C and under 26 - 30 bar of oxygen pressure. The effect of Ca²⁺ doping on the variation of oxygen content, structural chemistry and superconductivity for Ca-doped R247 phases was investigated. The upper limit of substitution of Ca²⁺ for R in R247 was determined to be 0.10, 0.10, and 0.04, for phases with R = Y, Dy, and Sm, respectively, as indicated by x-ray diffraction (XRD) data. The lattice parameters of Ca-doped R247 phases were found to vary insignificantly or decrease slightly upon Ca doping and these observations were attributed to the possibility of dual substitution of Ca²⁺ for both R³⁺ and Ba²⁺ sites. However, the corresponding orthorhombicity was found to increase or vary insignificantly. Upon Ca²⁺ doping the superconducting transition temperature (Tc) of R247 phases was found to decrease or increase from 93.8 K, 83.4 K and 64.5 K to 90.3 K (x = 0.10), 86.8 K (x = 0.10), and 72.2 K (x = 0.04) for phases with R = Y, Dy, Sm, respectively. Oxygen content or hole concentration (nh) of Ca-doped R247 phases was found to decrease with increasing Ca²⁺ content, as indicated by the iodometric titration data. The variation of Tc, sites of substitution and oxygen compositions for the title Ca-doped R247 phases will be discussed. |
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