High Tc superconductivity in single crystal YBa2Cu3O7−δ

We report the structure and superconductivity of single crystal YBa2Cu3O7−δ. The maximum dimensions of single crystal are 2.5×2.5×1.5 mm3. It is orthorhombic structure with space group Pmmm, cell parameters are a =3.88 A , b =3.82 A , c =11.68 A . The superconducting critical temperature is Tc=91 K. And a resistance anomalous phenomenon is also observed at 280 K.