  The Rietveld refinement of the polycrystalline powders of 1% Fe and Mn-doped
(Na0.5Bi0.5)0.94Ba0.06Ti0.98V0.02O3 at the Ti-site confirmed a single
rhombohedral (R3c) phase. The bandgap, (Eg) was affected by the anti-phase
octahedral tilt angle and the spin-orbit splitting energy of Ti4+2p3/2 and
Ti4+2p1/2 states. The decrease in Bi loss and increase in the binding energy of
Ba due to Fe/Mn doping has been correlated to the strengthening of Bi-O and
Ba-O bonds which was revealed from the XPS studies thereby further related to
the average A-O bond length from structural studies. Hence, a reduction of
oxygen vacancy (VO) for the doped samples has been justified. A significant
improvement of the dielectric constant, relaxation time ({\tau}0), and the
decrease in conductivity due to doping was revealed from the
frequency-dependent (10Hz-1MHz) dielectric measurement study. The conduction
and relaxation process is dominated by the short-range movement of defects. The
activation energy (Ea ~1eV) revealed that there is a presence of double-ionized
VOs. The ECE study showed a significant enhancement of the changes in entropy,
and the adiabatic temperature difference due to doping, with the change in
tempearture being highest in the Fe-doped sample. Such improvement of
dielectric and ECE properties was confirmed due to the reduction of the
mobility of oxygen vacancy because of the formation defect dipoles.
