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Observation of bond enthalpy dependence of insulating character in rare earth substituted BiFeO3

The temperature dependence of impedance and dielectric properties of BiFeO3 (BFO) and Bi0.90R0.10FeO3 (where R  =  La, Nd, Eu, Gd and Ho) compounds were investigated. The detailed impedance studies indicated that substitution of rare earth elements significantly enhanced the insulating character of BFO. The enhancement of insulating character was attributed to the improved grain and grain boundary resistances in the substituted compounds. A systematic variation of grain and grain boundary resistances, relaxation times and activation energies in Bi0.90R0.10FeO3 compounds was observed and explained based on the concept of bond enthalpy. The dielectric anomaly in BFO around the temperature 493 K got suppressed with the substitution of rare earth elements and the amount of suppression was discussed on the strength of R–O bond enthalpies. The impedance, ac conductivity and dielectric data corroborated with the idea that the insulating character in Bi0.90R0.10FeO3 compounds was strongly dependent on the strength of bond enthalpies of R–O bonds.