Preparation of thin-film oxide superconductor, Y1Ba2Cu3O7-δ by facing-targets sputtering deposition

Thin-film oxide superconductor, Y1Ba2Cu3O7-δ was prepared onto single-crystal MgO (100) substrates by facing-targets sputtering (FTS) deposition technique. Throughout the various preparation conditions, little deviation of the compositional ratios of the metallic elements in the as-prepared films from those of the targets: i.e. Y:Ba:Cu = 1:2:3 was observed. The atomic structures and properties of the superconductivity of the as-prepared films largely depended on the substrate temperature, Ts. They were classified as the following five regions. Region I: 720 degrees C > Ts > 670 degrees C. The films had c-axis oriented Y1Ba2Cu3O7-δ structure having Tc0 > 70 K. Region II: 670 degrees C > Ts > 630 degrees C and 770 degrees C > Ts > 720 degrees C. The polycrystalline Y1Ba2Cu3O7-δ having Tc0 ∼ 40 K was observed. Region III: 800 degrees C > Ts > 770 degrees C and 530 degrees C > Ts > 400 degrees C. A different crystalline structure having ca. 1/3 periodicities of the c-axis length of Y1Ba2Cu3O7-δ appeared. It had semiconductor-like temperature dependence of the electric resistivity. Region IV: 630 degrees C > Ts > 530 degrees C. A transition region between Regions I and III. The polycrystalline Y1Ba2Cu3O7-δ and the 1/3 periodicity structures coexisted. Region V: 400 degrees C > Ts > R.T. The films were amorphous and electrically insulating. In this paper the dependence of the structure on Ts is explained by two factors which govern the crystal growth process