Tuning of BiFeO3 multiferroic properties by light doping with Nb

Abstract

BiFeO3, as one of few multiferroic perovskites, is distinguished by some drawbacks such as high leakage current, low remnant magnetic polarization, high electric coercive field, and difficulties of pure phase synthesis that still keep it away from any practical use in electronics. There have been many attempts to improve the overall properties of BiFeO3 by A- or B-site doping or by both. It was found that B-site doping with Nb can potentially improve both the ferroelectric and magnetic properties of BiFeO3. In this study, BiFe1–xNbxO3 (x=0.002; 0.005 and 0.01) bulk ceramics were investigated in the quest for a more integral understanding of changes in multiferroic properties caused by light Nb doping (≤ 1 mole%). BiFe1–xNbxO3 powders were synthesized by hydro evaporation method and only traces of the secondary phases were observed. Multiferroic properties of bulk ceramics were investigated using X-ray diffraction (XRD) analysis, scanning electron spectroscopy (SEM), polarization (PMTS), and magnetization (SQUID) techniques. It was shown that even small percentages of Nb could notably change the electric and magnetic behavior of BiFeO3. The electric conductivity differed by two orders of magnitude between samples doped with 0.2 and 1% Nb. The ferroelectric behavior strongly depended on the conduction mechanism, and the transition from space-charge-limited current (SCLC) conduction to trap-filled Limited (TFL) conduction regime reflected on a change in hysteresis patterns, particularly for the samples with 0.2 and 0.5% Nb. ZFC-FC magnetization curves were separated for all Nb concentrations and the degree of separation increased with Nb doping. Weak ferromagnetic behavior was observed from the hysteresis measurements and the increase of remnant magnetization with Nb concentration. The coercive magnetic field changed drastically compared to the pure BiFeO3, namely, the sample with 1% Nb exhibited a very high coercive magnetic field of ~10 kOe.