Structural, magnetic, electrical and optical properties of Aurivillius phase Bi6Fe1.5Co0.5Ti3-W O18 (0 ≤ x ≤ 0.07) ceramics

Abstract

In this paper, we investigated the structural, multiferroic, dielectric and optical properties of Aurivillius Bi6Fe1.5Co0.5Ti3-xWxO18 (0 ≤ x ≤ 0.07) ceramics. The doping of W6+ ions promoted the grain’s growth and induced c-axis orientation. The remnant magnetization Mr monotonously decreased from 0.49 to 0.13 emu/g with increasing the doping level from 0 to 0.07, which was primarily attributed to the reduced Fe2+-O-Fe3+ exchange and the improved orientation growth. The remnant polarization Pr increased from 4.5μC/cm2 for x = 0–8.3μC/cm2 for x = 0.05 and then decreased to 7.2μC/cm2 for x = 0.07, the enhanced ferroelectricity was mainly related to the suppressed oxygen vacancy and larger grain size, while the weakened ferroelectricity was ascribed to the improved c-axis orientation. The Mr (0.23 emu/g) along c axis was larger 0.13 emu/g in ab plane while the Pr (7.2μC/cm2) along c axis was smaller than 9.3μC/cm2 in ab plane in x = 0.07, which demonstrated the anistropy of multiferroicity. In addition, all samples exhibited two different dielectric relaxations. The first one with activation energy ranging from 0.47 to 0.53 eV was assigned to the hopping process of electron, while the second one with activation energy varied from 1.45 to 3.63 eV was associated with the viscous motion of ferroelectric domain walls. Two direct absorption edges were demonstrated by Tauc’s law in all samples. The band gap 1 increased from 1.93 to 1.95 eV due to the lower t2 g state of Fe2+. The band gap 2 varied between 2.21 and 2.28 eV, which was proposed to the competition between TiO6 distortion and Ti4+ content. These results indicate that doping donor W6+ in Aurivillius compounds is a feasible way to regulate the multiferroic and optical properties.