Oxygen vacancy-dependent multiferroic properties and the valence state of Fe in Bi6-xSmxFe1.4Ni0.6Ti3O18 ceramics prepared by combined combustion method

Sm-modified Bi6-xSmxFe1.4Ni0.6Ti3O18 (BSFNT- x) ceramics were prepared using the combined conbusiton method to investigate their multiferroic and dielectric properties. It is found that a structural phase evolution from an orthorhombic phase to a tetragonal one and then back to the orthorhombic phase over the doping range. The remanent polarization (2Pr) was increased up to 15.4 μC/cm2 when the Sm content is 0.30, which is attributed to the structural distortion and the oxygen vacancies induced by Sm modification. In the meanwhile, the remanent magnetization (2Mr) was also increased up to 1.9 emu/g in the BSFNT- 0.25 sample. The temperature spectra of the dielectric loss show the characteristics of dielectric relaxation from 120 K to 500 K, which can be ascribed to the electron-hopping between Fe3+ and Fe2+ ions. The XPS measurement indicates that a small amount of Sm modification enhances the inhibition of oxygen vacancies. However, the content of Fe2+ ions increases when Sm content is greater than 0.20.