Structural, electrical and magnetic characterisation of a new Aurivillius phase Bi5−xThxFe1+xTi3−xO15 (x = 1/3)

Abstract

A novel Aurivillius oxide with the composition Bi5−xThxFe1+xTi3−xO15 (x=1/3) has been successfully prepared by the conventional solid-state high-temperature synthesis. X-ray diffraction confirmed that the material is strictly single-phase and has a four-layer Aurivillius structure with the orthorhombic lattice (unit cell parameters: a=5.4300(2)Å, b=5.4451(7)Å, c=41.2800(6)Å; space group A21am (36)). Temperature dependent electrical and magnetic properties of the material have been investigated and compared to those of Bi5FeTi3O15. The relative permittivity maximum and divergence of loss tangent, observed at 970K, is attributed to a ferroelectric-to-paraelectric phase transition. At low temperature, the material exhibits paramagnetic behavior with short-range antiferromagnetic coupling. Analysis of Fe K-edge XAFS spectra showed that the Fe–O distances in Bi5−xThxFe1+xTi3−xO15 (x=1/3) are shorter and the general local environment of Fe is more distorted compared to Bi5FeTi3O15. In both compounds the Fe atom is shifted from the center of the oxygen octahedron towards one of its faces, giving rise to three shorter and three longer Fe–O distances.