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

The ceramics with the composition of Sr _xBi_{7− x}Fe_1.5Co_1.5Ti₃O_21−δ (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}Bi _mFe_{1− i}Co _iO_3−γ 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 (2 M_r) is 2.27 emu/g and the remnant polarization (2 P_r) is 2.89 μC/cm² at an applied electric field of 100 kV/cm for the x = 0.25 sample. [ABSTRACT FROM AUTHOR]