The microstructure of (Hg,Tl) -based high temperature superconducting films on LaAlO₃ substrates

The results of transmission electron microscopy (TEM) and X-ray microanalysis of a (Hg,Tl)Ba₂Ca₂Cu₃O_8+x (1223) thin film on a LaAlO₃ substrate are presented. The film was highly textured but polycrystalline, with c-axis oriented perpendicular to the substrate surface. The film/substrate interface was mostly sharp, but in some areas a 4-5 nm thick intermediate layer, of the (Hg,Tl)Ba₂Ca₁Cu₂O_6+x (1212) phase and an amorphous phase, was observed. CuO_x, BaCuO₂ and Ca-rich precipitates were found in the film. The intergrowth of other members of (Hg,Tl)-Ba-Ca-Cu-O compound family, in the form of stacking faults and ordered structures, were found to be common. Microstructural evidence suggested that texture was induced by surface energy/growth anisotropy, and initiated at the substrate surface more than at the free surface.