Abstract Fast ionic conduction through strain engineered heteroepitaxial film have been demonstrated well. However, this effect in the preferentially orientated film remains to be unexplored. Here, we report the effect of interatomic distance between cation-oxygen bonds on the oxygen ionic transport in preferetially (111) oriented Ce0.80Sm0.1M0.1O2-δ (M = Gd, Nd, Pr, La) film over an amorphous quartz substrate. With the increase in ionic radii of dopant cation, the films exhibited a substantial increase in tensile strain with a change in lattice constant (Δa) in the order of ∼1.14% (Δa: 1.14% (Sm3+ + La3+) > 1.04% (Sm3+ + Pr3+) > 0.69% (Sm3+ + Nd3+) > 0.14% (Sm3+) > 0.08% (Sm3+ + Gd3+)) has strong influence on defect association enthalpy (ΔHa) leading to the change in migration energy of oxygen ion during conduction process. Highest conductivity was observed from Ce0.85Sm0.1Nd0.1O2-δ, which is four times greater than that of Ce0.85Sm0.2O2-δ. As a consequence, it is clear that optimum co-dopant is needed to attain the critical ionic radii/tensile strain to achieve the maximum ionic conductivity in the preferentially oriented ceria-based thin film. This work demonstrates the importance of tuning the ionic radii of dopant cation, which can effectively facilitate the optimum expansion of lattice to attain the fast ionic conduction process in (111) oriented thin film based solid electrolyte.