Phase Control of Superconducting Bi-Sr-Ca-Cu-O Thin Films Prepared by Laser Ablation Method

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Abstract
Three phases of Bi2Sr2Ca n-1Cu n O2n+4 superconductors, i.e., Bi2Sr2Cu1O6(2201), Bi2Sr2Ca1Cu2O8(2212) and Bi2Sr2Ca2Cu3O10(2223), have been controlled by a laser ablation method. The 2201, 2212 and 2223 phases are selectively formed by controlling the substrate temperature, the starting composition of targets and the ambient pressure. The oxygen partial pressure plays an important role in these three parameters. Under a pressure higher than 6×10-2 Torr, the 2201 phase is dominantly formed in the wide range of substrate temperature and composition. Under a lower oxygen partial pressure (from 3×10-3 to 6×10-2 Torr), on the other hand, the control of the three phases, 2201, 2212 and 2223, is possible for as-deposited films only by changing the target compositions. For the 2212 thin film, Cu-rich samples show good superconducting behavior, while particles are observed on the film surface. The surface morphology of the thin film becomes better for the Cu-poor and Bi-rich samples.