  We study the effect of the growth orientation on the structural, electronic,
and hence transport properties of Sr$_2$CoNbO$_6$ thin films grown on the
orthorhombic NGO(100) and cubic MgO(100) substrates. The x-ray diffraction
patterns show the growth of the thin film along $a$-axis resulting in the
asymmetric ($b\neq c$) in-plane compressive strain in case of NGO(100), whereas
along $c$-axis with tensile strain in case of MgO(100) substrate. The
temperature dependent resistivity measurements indicate the lower electronic
conductivity for the film grown on the NGO(100) substrate, which is found to be
correlated with the higher degree of the oxygen deficiencies and hence larger
concentration of the insulating Co$^{2+}$ in this sample. Further, the x-ray
photoemission spectroscopy measurements show that Sr and Nb are present in the
2+ and 4+ valence state, whereas Co exist in the 2+, 3+ as well as 4+ states,
fraction of which was found to vary with the growth orientation. Moreover, the
analysis of leakage current using the sum exponent model indicate the presence
of two different relaxation mechanisms in these samples.
