Growth and microstructure of Bi-Sr-Ca-Cu-O thin films

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Abstract
Thin superconducting Bi-Sr-Ca-Cu-O films have been grown by reactive magnetron sputtering with an average cation ratio of 2:2:1:2 on single-crystal (100)MgO. Films show a superconducting transition onset at 117 K, but do not go to zero resistance until 83–84 K. Secondary electron microscopy and electron beam microprobe showed two major phases with different compositions and morphologies. The dominant phase was a lamellar phase with composition very close to the 2:2:1:2 cation ratio. The second phase had a needle-like morphology, which was deficient in Bi, and had excess Cu. The nonsuperconducting Sr14−xCaxCu24O41 phase had been known to exist in bulk; therefore, the needle phase could be an intermediate step in the formation of Sr14−xCaxCu24O41 phase as Bi deficiency in the needles increased with increasing annealing temperature and/or time.