Microstructure and Its Heat Treatment Process of Thin Films Fabricated by Alternate Sputtering of (Bi,Pb)2Sr2CaCu2O x  and Pb–Ca–Cu–O Targets on SrTiO3 Substrates

Satoshi Hata,Hikaru Saito,Daiki Fukuda,Zimeng Guo,Hitoshi Kitaguchi,Hideharu Nakashima,Yusuke Shimada,Akiyoshi Matsumoto

doi:10.1109/tasc.2023.3259920

Abstract

For obtaining microscopic knowledge toward a fabrication process of (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x (Bi,Pb-2223) single-phase material, we fabricated a multilayered film on a SrTiO 3 (001) substrate by a sputtering method using (Bi,Pb) 2 Sr 2 CaCu 2 O <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y (Bi,Pb-2212) and Pb–Ca–Cu–O targets alternately at 650˚C. The as-grown film was an epitaxially grown multilayered film consisting of Bi,Pb-2212 and Pb–Ca–Cu–O layers. Coarse grains of impurity phases were also formed within the multilayered film, and these impurity phases were difficult to eliminate even after heat treatments. After 10 h heat treatment at 840°C with Bi,Pb-2223 pellets, the phase transition from Bi,Pb-2212 to Bi,Pb-2223 occurred in the multilayered film. The phase transition to Bi,Pb-2223 proceeded preferentially at the interface with the impurity phases and the Pb–Ca–Cu–O layers. These observation results suggest that the impurity phases promote three-dimensional atomic diffusion in the multilayered film to accelerate the phase transition to Bi,Pb-2213, as well as consume constituent elements, Ca, Cu and O. Even after the 100 h heat treatment at 840°C with Bi,Pb-2223 pellets, the phase transition from Bi,Pb-2212 to Bi,Pb-2223 did not proceed completely, and the fraction of the Bi,Pb-2223 phase in the whole superconducting phases was ∼50%. It is suggested that controlling the formation and microstructure of the impurity phases is a key to further increasing the fraction of the Bi,Pb-2223 phase.

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