Polaronic transport in the ferromagnetic phase of Gd1−xCaxBaCo2O5.53

► Synthesis of phase pure Gd1−xCaxBaCo2O5.5 series of samples (0≤x≤0.25). ► Ca substitution results in introduction of Co4+. ► Co4+ helps nucleate polarons in the system that dominates the transport behaviour. ► Polaron transport is associated with the ferromagnetic state of the sample.