For growth of high-quality epitaxial thin films of high-temperature superconductors (HTSCs), it is essential to choose appropriate substrates. For a thin film of La2-xMxCuO4 (M=Ba, Sr), the superconducting transition temperature (Tc) is modified by the strain due to the lattice mismatch between the film and the substrate. For the compressively strained (001) films of La2-xSrxCuO4 and La2-xBaxCuO4 on LaSrAlO4 substrates, Tc reached 44 and 47 K, respectively, which are higher than the values for bulk samples. Moreover, the Tc-x phase diagrams for the compressed films did not show a local minimum at x∼0.125, the so-called "1/8 anomal". Based on the experimental results, we suggest that the reduction of antiferromagnetic spin fluctuation increases Tc in HTSCs. For thin films of Bi2Sr2CaCu2O8, we foun d that substrates with a small lattice mismatch are very effective in attaining a smooth and almost precipitate-free surface.
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