  Transition metal oxide thin films show versatile electrical, magnetic, and
thermal properties which can be tailored by deliberately introducing
macroscopic grain boundaries via polycrystalline solids. In this study, we
focus on the modification of the magnetic and thermal transport properties by
fabricating single- and polycrystalline epitaxial SrRuO3 thin films using
pulsed laser epitaxy. Using epitaxial stabilization technique with atomically
flat polycrystalline SrTiO3 substrate, epitaxial polycrystalline SrRuO3 thin
film with crystalline quality of each grain comparable to that of
single-crystalline counterpart is realized. In particular, alleviated
compressive strain near the grain boundaries due to coalescence is evidenced
structurally, which induced enhancement of ferromagnetic ordering of the
polycrystalline epitaxial thin film. The structural variations associated with
the grain boundaries further reduce the thermal conductivity without
deteriorating the electronic transport, and lead to enhanced thermoelectric
efficiency in the epitaxial polycrystalline thin films, compared with their
single-crystalline counterpart.
