Size and Lone Pair Effects on the Multiferroic Properties ofBi0.75A0.25FeO3−δ(A = Sr, Pb, and Ba) Ceramics

Abstract

The work presents a comparative study of the effects of divalentBa,Sr, andPbsubstituents on the multiferroic properties ofBiFeO3. The multiferroic properties ofBi0.75A0.25FeO3(A = Sr,Pb,Ba) solid solution have been explained taking into account the effects of size differences and electronic configuration differences between the host element (Bi) and the substituent. X‐ray diffraction studies revealed thatSrandPbsubstitution atBi‐site transforms the rhombohedral phase (R3c) to cubic phase (Pm3m), whereas the Ba‐substituted sample exhibited the presence of both rhombohedral and cubic phases (R3c + Pm3m). Electronic structure studies throughXPSrevealed that charge imbalance induced by divalent substitution was being compensated by the formation of oxygen vacancies, while theFeions exist inFe2+andFe3+states. Replacement of volatileBibySr,Pb, andBareduces the concentration of oxygen vacancies (VO2+) and helps to improve the dielectric properties. Strong magnetization enhancement was observed in the substituted compositions and was seen to be consistent with the suppression of cycloid spin structure due to structural transformation as well as possible changes inFe–Olocal environment leading to local lattice distortion effects. Furthermore, the observed decrease in the values of magnetic coercivity at low temperature in all the substituted samples is explained in terms of reduced effective single ion anisotropy, originating in the magnetoelectric coupling and being a particularly stronger effect in the case of the lone pair dopantPb, consistent with theoretical predictions. The lone pair substituentPbleads to the largest dielectric constant, enhanced magnetization, and large effects on the low‐temperature hysteresis.