Microstructural and physical characterizations of (1-x)(0.67BiFeO₃+ 0.33BaTiO₃+ 1%MnO₂)− x(CoFe₂O₄+ 3%ZnO) magnetoelectric composites

BiFeO₃ (BFO) was mixed with BaTiO₃ (BTO) to form a solid solution of large piezoelectric coefficient (d₃₃) for the fabrication of magnetoelectric (ME) composites with the Zn-doped CoFeO₄ (CFO). The 0.67BFO+0.33BTO solid solution, which was doped with 1 at% MnO₂ for lowering leakage current, showed a high d₃₃ of 121 pC/N. However, in the composites made with CFO, a much lower d₃₃ (<42 pC/N) was retained. The microstructure of the composites was featured by the large CFO grains (∼5 μm) embedded in the 0.67BFO+0.33BTO matrix of much finer grains (∼0.5 μm). The CFO grains each had a well-defined morphology with clear boundary discriminating them from the neighboring piezoelectric phase. Both the CFO and piezoelectric grains showed a high crystallinity as indicated by the appearance of clear Kikuchi patterns in electron backscattered diffraction. After reducing DC conductivity of CFO by Zn-doping and the optimization of fractional ratio of the Zn-doped CFO in the composites, a ME voltage coefficient of 81.8 mV/cm-Oe was achieved, which was high among the lead-free particulate ME composites prepared by the conventional solid-state sintering.