Substitutional effect of bismuth ferrite on the electrical properties of sodium bismuth titanate ceramics

Lead free sodium bismuth titanate ceramics was substituted with bismuth ferrite in low mole fraction and the influence of substitution on the dielectric constant, Curie temperature, depolarization temperature, remnant polarization, coercive field and piezoelectric coefficient were studied. Rhombohedral R3c symmetry is maintained for all mole fractions. Dielectric constant decreases and small deviation arises in Curie temperature on bismuth ferrite substitution. No significant change in depolarization temperature (Td) is observed on bismuth ferrite substitution. Spontaneous and remnant polarization increases and piezoelectric coefficient is enhanced up to x = 0.01 mol fraction and then decreases. Also coercive field decreases up to x = 0.01 mol fraction and then increases. Reduced remnant polarization, dielectric constant and increased coercive field are due to hardening effect induced by the acceptor Fe3+ cation in the B-site of sodium bismuth titanate. Formation of Ti4+ cation and oxygen vacancies restricts domain wall motion and suppresses domain reorientation which decreases the extrinsic contribution to piezoelectric coefficient and hence d33 decreases.