Structural Evolution and Multiferroics in Sr‐Doped Bi 7 Fe 1.5 Co 1.5 Ti 3 O 21 Ceramics

The ceramics with the composition of Sr x Bi 7− x Fe 1.5 Co 1.5 Ti 3 O 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 m Fe 1− i Co i O 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 SBFCT s 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/cm 2 at an applied electric field of 100 kV/cm for the x = 0.25 sample.