Growth of Ca-Doped Large Grain GdBaCuO Superconductors

Authors

  • Ling Cheng,

    1. Department of Physics, Key Laboratory of Artificial Structures & Quantum Control, Ministry of Education, Shanghai Jiao Tong University, Shanghai, China
    Search for more papers by this author
  • Wei Li,

    1. Instrumental Analysis Center, Shanghai Jiao Tong University, Shanghai, China
    Search for more papers by this author
  • Bin Quan Kou,

    1. Department of Physics, Key Laboratory of Artificial Structures & Quantum Control, Ministry of Education, Shanghai Jiao Tong University, Shanghai, China
    Search for more papers by this author
  • Xin Yao,

    Corresponding author
    1. State Key Laboratory for Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai, China
    • Department of Physics, Key Laboratory of Artificial Structures & Quantum Control, Ministry of Education, Shanghai Jiao Tong University, Shanghai, China
    Search for more papers by this author
  • Hiroshi Ikuta

    1. Department of Crystalline Materials Science, Nagoya University, Nagoya, Japan
    Search for more papers by this author

Author to whom correspondence should be addressed. e-mail:xyao@sjtu.edu.cn

Abstract

The effect of calcium doping on growing GdBa2Cu3Oz (GdBCO or Gd123) bulk superconductors using top-seeded melt-textured growth (TSMTG) method in air was studied. NdBCO thin films deposited on MgO substrate were effectively used as cold-seeds because of their superheating natures, which allow them enduring a higher maximum processing temperature (Tmax) than that of a conventional TSMTG process. Several heavily Ca-doped GdBCO (up to 3 wt% CaCO3) single domains were obtained without heterogeneous nucleation. Moreover, an interesting phenomenon of negative growth was observed during the cooling-down process of CaGdBCO, which prevented the grain from further crystallization. The compositional analysis revealed that the Ca content has a declined tendency from the initial growth region toward the edge. It is deduced that the effective Ca distribution coefficient k > 1, which gives rise to a decreased peritectic temperature (Tp) with the reduction of the Ca content, is the main origin of the negative growth behavior. To overcome this obstacle, a two-stage cooling procedure was developed, i.e., slow cooling followed by fast cooling, to compensate the loss of the growth driving force caused by the decrease of Tp. Consequently, a highly doped CaGdBCO bulk was grown with a size of 14 mm2.

Ancillary