Structural Evolution and Multiferroics in Sr-Doped Bi7Fe1.5Co1.5Ti3O21 Ceramics

The ceramics with the composition of Sr(x)Bi(7-x)Fe(1.5)Co(1.)5 Ti3O21-delta (0 <= x <= 1, SBFCT) were prepared by a citrate-nitrate combustion method, and the phase evolution with an increasing Sr content was investigated. Pure Aurivillius phase SBFCT with a layer number of n = 6 was obtained when x <= 0.25, and then the structure collapsed to 5 layers for x = 0.50, then alternating 4 and 5 layers for x = 0.75, and finally 4 layers for x = 1.00. Meanwhile, secondary phase Sr(1-m)BimFe(1-i)Co(i)O(3-gamma) appeared when x > 0.25, which is antiferromagnetic (AFM) and with low resistivity. Enhanced ferromagnetic and ferroelectric properties were observed from single phase SBFCTs at the room temperature, and the ferromagnetic transition temperature (T-c) increases with the Sr doping level x in the single phase range. The remnant magnetization (2M(r)) is 2.27 emu/g and the remnant polarization (2P(r)) is 2.89 mu C/cm(2) at an applied electric field of 100 kV/cm for the x = 0.25 sample.