Electrical properties of stoichiometric BiFeO3 prepared by mechanosynthesis with either conventional or spark plasma sintering

Phase-pure powders of stoichiometric BiFeO3 have been prepared by mechanosynthesis. Ceramics sintered by either conventional heating in air or spark plasma sintering (SPS) followed by oxidative anneal in air are highly insulating with conductivity e.g. ~10 Scm at 300 °C and activation energy 1.15(2) eV, which are comparable to those of a good-quality BiFeO3 single crystal. By contrast, the as-prepared SPS sample without the post-sinter anneal shows higher conductivity e.g. ~10 Scm at 225 °C and lower activation energy 0.67(3) eV, indicating some reduction of the sample by the SPS process. The reason for the high conductivity observed in some ceramic samples reported in the literature appears to be unclear at present. Introduction Bismuth ferrite (BiFeO3) is one of the most studied multiferroic ceramics since multifunctional properties are present at room temperature; it exhibits a G-type antiferromagnetic order up to the Néel temperature at ~360 oC and ferroelectric order up to the Curie temperature at ~ 830 oC. [1, 2] However, phase-pure bulk BiFeO3 is notoriously difficult to synthesise and it is very common that small amounts of persistent secondary phases, mostly Bi2Fe4O9 and Bi25FeO39, are present. Thus, although many methods have been proposed in the literature [3–19] to obtain phase-pure bulk BiFeO3, only few have been successful.