Microstructure and Its Heat Treatment Process of Thin Films Fabricated by Alternate Sputtering of (Bi,Pb)2Sr2CaCu2Ox and Pb–Ca–Cu–O Targets on SrTiO3 Substrates
IEEE Transactions on Applied Superconductivity（2023）
Abstract
For obtaining microscopic knowledge toward a fabrication process of (Bi,Pb)
2
Sr
2
Ca
2
Cu
3
O
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
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-2223, 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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Key words
(Bi,Pb) $_{2}$ Sr $_{2}$ Ca $_{2}$ Cu $_{3}$ O $_{x}$ (Bi,Pb-2223) superconductor,electron microscopy,heat treatment,microstructure,thin film
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