Superconductivity and Crystal Structure of the Y 1 Ba 2 Cu 3 O 7-y -WO 3 System

The relationship between the superconductivity and crystal structure of the Y 1 Ba 2 Cu 3 O 7- y -WO 3 system has been studied. Tungsten oxide has various oxidized states, and mixed WO 3 in YBCO easily donates its oxygen atoms to YBCO. It is found that the orthorhombic structure of YBCO is modified by mixing of WO 3 . The lattice constant a increases with increasing concentration of WO 3 , while the others, b and c , do not significantly change. Although the atomic arrangement in the Cu(2)-O plane of YBCO is consequently modified, superconducting transition temperature T c is kept nearly constant.