中文摘要：

用固相工艺制备了Bi6Fe2-xCoxTi3O18（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,2Ms约为4.49 emu/g,BFCT-1.0具有最高的剩余磁化强度,2Mr约为0.89 emu/g.Co含量在0.2 x 1.2范围内,随着Co含量的增加样品顺磁—铁磁相变温度从752K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.

英文摘要：

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 Bi6Fe2-xCoxTi3O18（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 0.6and 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-2.0samples 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 2Ms and 2Mr have been recorded. Both the 2Ms and 2Mr 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（TMC） decreases from 752 to 372 K.At RT, the BFCT-x samples are ferroelectric, and the maximum and minimum values of remnant polarization（2Pr）are about 8.0 μC/cm2（x = 0.6） and 1.1 μC/cm2（x = 1.2）, respectively. The 2Pr of the BFCT-0.6 is about three times larger than that of Bi5Fe2Ti3O18（x = 0） sample. Furth