Effect of Nb and more Fe ions co-doping on the microstructures, magnetic, and piezoelectric properties of Aurivillius Bi₅Ti₃FeO₁₅ phases

Aurivillius Bi₅Ti_3−2xFe_1+xNb_xO₁₅ (BTFNO, x = 0.1, 0.2, 0.3, and 0.4) phases were prepared by solid state reaction method. The structures and dielectric responses were studied, and especially the effects of Nb with a higher valence and more Fe co-doping on the magnetic and piezoelectric properties were addressed in detail. The BTFNO samples were well crystallized with no detectable impurities, and plate-like microstructures with various sizes demonstrate the typical characteristics of bismuth-layer Aurivillius materials. It is found that a dielectric loss peak appears in the Nb and Fe co-doped Bi₅Ti₃FeO₁₅ (BTFO) ceramics, and it has a shift towards a lower frequency with increasing the Nb doping contents. Furthermore, antiferromagnetic long-range magnetic order is improved with the introduction of Nb and more Fe co-doping. And compared with that of the parent BTFO forms, a clear discrepancy, which is indicative of a super-paramagnetic behavior, of the magnetization vs. temperature curves in zero-field cooling and field cooling cases is observed by the introduction of the Nb and more Fe ions. More interestingly, the introduction of Nb and more Fe ions can suppress the preferred c-axis growth while promoting the a-/b-axis growth of the plate-like grains, and thus favors the piezoelectric behaviors of the BTFO Aurivillius phases along the growth orientation.