Crystal structure of Bi4-xCexTi3O12(x=0, 0.25, 0.5 and 0.75) studied by Raman spectroscopy and neutron powder diffraction

Abstract

Structural refinement using both neutron powder diffraction data and Raman spectroscopy were carried out to determine the site preference of Ce atoms and structural changes in Bi4-xCexTi3O12 (x=0, 0.25, 0.5 and 0.75) compounds. In the Raman spectroscopic study, the peak at 65 cm(-1) of Bi4Ti3O12 (BTO), assigned to the Bi-O bonds in the Bi2O2 layers, did not shift or shifted to 63 cm(-1) after Ce incorporation. However, the peaks of BTO at 119 and 148 cm(-1), assigned to the Bi-O bonds in the perovskite units, became diffusive and moved to higher frequencies of (121 and 150 cm(-1)), (123 and 152 cm(-1)) and (125 and 157 cm(-1)) when x was 0.25, 0.5 and 0.75, respectively. From the Raman spectroscopic study, the substitution sites of the Ce atoms were determined to be only the Bi sites in the perovskite units. The peaks originated from the TiO6 octahedrons moved to higher frequencies and merged with the neighbouring peaks, indicating relaxation of distortion of TiO6 octahedrons with increase in x. Structural refinement results showed that the a-axis lattice parameters decreased with increase in x, while the b-axis lattice parameters did not exhibit significant changes and the c-axis lattice parameters decreased. Decrease in orthorhombicity with increasing x showed the relaxation of structural distortion of TiO6 octahedrons. Spontaneous polarization was calculated based on the refinement results, which decreased from 35.4 to 30.4, 27.5 and 16.5 mu C cm(-2) when x is 0, 0.25, 0.5 and 0.75, respectively.