Co含量对Bi6Fe2-xCoxTi3O18样品多铁性的影响

用固相工艺制备了Bi₆Fe_2-xCo_xTi₃O₁₈ (BFCT-x, x=0, 0.2, 0.6, 0.8, 1.0, 1.2, 1.6, 1.8, 和2.0)多铁陶瓷样品, 样品X射线谱分析发现, 随着Co含量的增加, 样品晶格常数出现了先增大后减小的变化. 室温下, BFCT-0.6样品呈现出相对较高的饱和磁化强度, 2M_s约为4.49 emu/g, BFCT-1.0具有最高的剩余磁化强度, 2M_r约为0.89 emu/g. Co含量在0.2 ≤x≤qslant 1.2范围内, 随着Co含量的增加样品顺磁–铁磁相变温度从752 K降至372 K. 小量的Co改善了样品的铁电性能, 当x=0.6时样品样品的铁电性能最佳, 随着含量增大样品铁电性能下降, 但当x >1.2时样品的铁电性能又得到了改善.

Effects of Co-doping on multiferroic properties of Bi6Fe2-xCoxTi3O18 ceramics

Multiferroic materials have drawn increasing interest due to the coexistence of ferromagnetism (FM) and ferroelectricity (FE), which provides significant potentials for applications in spintronics, information storage, and sensors, etc. In this paper, the multiferroic Bi₆Fe_2-xCo_xTi₃O₁₈ (BFCT-x,x=0-2.0) ceramics are prepared by the solid-state reaction. The BFCT-x samples belong to Aurivillius structure containing five perovskite layers clapped between two Bi-O layers. The lattice constants a, b, and c of BFCT-x samples increase simultaneously with increasing cobalt content up to 0.6 and then decrease with further addition of cobalt. The magnetic and ferroelectric properties, and their corresponding Curie temperatures are measured. At room temperature (RT), the magnetism of the BFCT-0, BFCT-1.8 and BFCT-2.0 samples can be understood by the presence of the antiferromagnetic (AFM) interaction with the dominant paramagnetism (PM) state, which is consistent with the linear behavior of the M-H plot. The Fe³⁺-O-Fe³⁺ and Co³⁺-O-Co³⁺ interactions present in the BFCT-x samples lead to AFM. The BFCT-0.2–1.0 samples show saturated magnetic loops, while the BFCT-1.2 sample is far from saturation even under an applied magnetic field of 10 kOe. The M-H curve of BFCT-1.6 sample shows a weak ferromagnetism. The Co content (x=0.2-1.6) dependences of 2M_s and 2M_r have been recorded. Both the 2M_s and 2M_r experience first-increase-then-decrease variation tendency with their maximal values of ～ 4.49 emu/g and ～ 0.89 emu/g located at x =0.6 and x =1.0, respectively. As the cobalt content varies from x=0.2 to x=1.2, the paramagnetic-ferromagnetic phase transition temperature (T_MC) decreases from 752 to 372 K. At RT, the BFCT-x samples are ferroelectric, and the maximum and minimum values of remnant polarization (2P_r) are about 8.0 μup C/cm² (x=0.6) and 1.1 μup C/cm²(x=1.2), respectively. The 2P_r of the BFCT-0.6 is about three times larger than that of Bi₅Fe₂Ti₃O₁₈ (x=0) sample. Furthermore, the dependence of 2P_r on Co content first increases with Co doping when x ≤qslant 0.6, and decreases from x=0.8 to x=1.2, and then increases again. The ferroelectric Curie temperature T_c of the BFCT-x samples increases with increasing x up to 0.8 and then decreases with further increasing cobalt content. It is noteworthy that the T_c of BFCT-1.0 is 2 K lower than that of BFCT-0.6, while the 2P_r decreases by 63%. It is seen that the 2P_r and 2M_r increase simultaneously with increasing Co content (below 0.6). When 0.8 < x ≤qslant 1.0, the 2M_r increases while 2P_r decreases with increasing Co content. After x>1.2, the 2M_r decreases while 2P_r increases with increasing Co content. The repelling between the FE and FM as discussed above may result from the magnetic-crystalline and ferroelectric-crystalline anisotropy. The mechanism of this phenomenon is not quite clear and needs further investigation.