Grain and grain boundary effects in Ca²⁺ doped BiFeO₃ multiferroic ceramics

Abstract

The present work reports the analysis of temperature‐dependent electrical and conductivity studies on Ca2+ doped BiFeO3 multiferroic ceramics in the temperature range of 300–600 K. The effect of Ca2+ doping on the impedance and modulus behavior of BiFeO3 lattice is discussed. The observed changes as a function of increasing Ca2+ concentration have been explained using the change in crystal unit cell. It is also shown that the microstructure changes significantly as a function of Ca2+ concentration. The grain and grain boundary effects in determining the impedance behavior is also reported in the paper.

Tactics of particle size for enhanced multiferroic properties in nanoscale Ca‐doped BiFeO3

“…This implies that charge compensation by Fe 4þ significantly decreases the T N . However, when charge neutrality exists due to oxygen vacancies T N enhances by 0.77K per 1% mol Cadoping [15]. Therefore, in the present system charge neutrality mechanism occurs via creation of oxygen vacancies.…”

“…The reason may be explained by the charge compensation mechanism through creation of oxygen vacancies on doping of divalent Ca 2þ ions at trivalent site (Bi 3þ ) [14]. Both of these ions being non-magnetic in nature have not direct contribution towards magnetism but due to different valences a charge imbalance is created in the system, which is balanced by either of two mechanisms [14,15]: (i) creation of oxygen vacancies and (ii) transformation of Fe 3þ to Fe 4þ . Either or both of them may exist in the present system.…”

“…Either or both of them may exist in the present system. Two extremes namely, CaFeO 2.5 and CaFeO 3 in principle may exist, which involves totally opposite mechanisms and has different impact on magnetic transition temperature [15]. If former is the case, all charge balance takes place by oxygen vacancies and all iron ions stay in 3þ valence state.…”

“…When divalent ion (Ca 2þ ) substitutes trivalent ion (Bi 3þ ) charge imbalance is created in the system. Three possibilities exist to balance the charge [14,15]: (i) creation of oxygen vacancies; (ii) transformation of some of Fe 3þ into Fe 4þ ; and (iii) coexistence of two or more phases. It has been demonstrated that charge compensation takes place via the creation of oxygen vacancies and Fe 3þ preserves its oxidation state [16].…”

“…It has been demonstrated that charge compensation takes place via the creation of oxygen vacancies and Fe 3þ preserves its oxidation state [16]. It is reported that structural effects increase the magnetic transition temperature so that charge compensation mechanism occurs by formation of oxygen vacancies [15]. However, no studies on the particle size effects on the charge compensation mechanism of Ca-doped BiFeO 3 nanoparticles have been reported.…”