Model-based quantification of inter-/intra-grain electrical parameters, hopping polydispersivity, and local energy barrier profile of BiFeMnO3 synthesized by different methods

Abstract

The major challenge limiting the application of inorganic perovskite multiferroics is the presence of high conductivity, giving rise to extrinsic factors that suppress the intrinsic ferroelectric response. Therefore, it is vital to identify, control, and understand conductivity effects in these perovskite oxides. For this purpose, the electrical and dielectric responses of a well-known multiferroic, BiFeO3 (BFO), have been extensively studied. In the present study, the role of oxygen vacancies has been thoroughly investigated through their manipulation by synthesis techniques, heat-treatment protocols, and specifically selected high-valent B-site dopants. Both Mn substitution and the sol–gel preparation technique significantly reduce oxygen vacancy formation. Comprehensive dielectric, impedance, and conductivity analyses have shown that in the low-temperature region, direct hopping of charge carriers between Fe2+ and Fe3+ can be classified as short polaronic hopping. However, the hopping of electrons generated because of singly- and doubly-charged oxygen vacancies and the conduction of space charges at the grain boundaries exhibits the characteristics of long polaron hopping. A polydispersive nature of the various hopping mechanisms has been observed in the present study. The temperature dependences of grain resistance (arising from two different intra-grain hopping mechanisms) and grain boundary resistance have been studied and quantified through equivalent circuit analysis. Based on the activation energies calculated for the three identified thermally activated processes, a potential well diagram is proposed.