Raman and X-ray photoelectron scattering study of lanthanum-doped strontium bismuth titanate

The ferroelectric ceramics of lanthanum-doped SrBi4Ti4O15 (SrBi4 - xLaxTi4O15:SBLT-x, x = 0.00, 0.05, 0.10, 0.25, 0.50, 0.75 and 1.00) have been synthesized. Raman and XPS spectrum measurements have been carried out to analyze the La substitution site and the influence of La-doping on the crystal structure. The results suggest that La^3+ ions prefer to occupy the A site in the case of x =<0.10, and at higher content they tend to be incorporated into Bi2O2 layers. At La content greater than 0.10, the TiO6 octahedra linking to the Bi2O2 layers shrink and the structure distortion relaxes more drastically. The concentration of oxygen vacancy decreases with La-doping, and then saturates when La content is higher than 0.10. The La-doping content has a lower critical value of about 0.10 in comparison with La-doped Bi4Ti3O12, which may be attributed to the stable Sr^2+ ions at A sites of SrBi4Ti4O15.