  Ba(Fe1-xCox)2As2 superconducting thin films have been grown on SrTiO3,
(La,Sr)(Al,Ta)O3, LaAlO3 and YAlO3 (YAO) single crystal substrates by pulsed
laser deposition. All the films, except on YAO, have been grown epitaxially
without buffer layers. The films deposited on YAO contained 45 degree in-plane
rotated grains and showed a broad superconducting transition. The onset Tc of
the films is observed to increase from 16.2 K to 24.5 K with increasing c/a,
mainly due to a slight distortion of the AsFe4 tetrahedron. From this
correlation, we expect that higher superconducting transition temperatures than
24.5 K in a strained epitaxial film may be possible.
