Critical current, film thickness and grain alignment for spray-pyrolyzed films of TlBa₂Ca₂Cu₃O_x

X-ray diffraction rocking curves are used to measure the c axis alignment of TlBa₂Ca₂Cu₃O_x films grown on polycrystalline substrates with thickness varying from 3 to 10.5 μm. Films thicker than 3 μm are found to contain two layers: a well aligned (3.5° FWHM) bottom layer, and a poorly aligned (greater than 12° FWHM) top layer. Azimuthal scans show that the component with good long-range out-of-plane alignment retains its characteristic colony microstructure of local in-plane alignment as film thickness increases. The length dependence of the critical current density may be accounted for by assuming that all the supercurrent is carried by the well-aligned component.