Superconducting Materials Research Center,General Research Institute for Nonferrous Metal,Beijing 100088,China Superconducting Materials Research Center,General Research Institute for Nonferrous Metal,Beijing 100088,China National Center of Analysis and Testing for Nonferrous Metal and Electronic Materials,Beijing 100088,China National Center of Analysis and Testing for Nonferrous Metal and Electronic Materials,Beijing 100088,China Superconducting Materials Research Center,General Research Institute for Nonferrous Metal,Beijing 100088,China Superconducting Materials Research Center,General Research Institute for Nonferrous Metal,Beijing 100088,China;