Raman scattering investigations on lanthanum-doped Bi4Ti3O12–SrBi4Ti4O15 intergrowth ferroelectrics

The ferroelectric ceramics of Bi4Ti3O12, SrBi4Ti4O15, and lanthanum-doped Bi4Ti3O12–SrBi4Ti4O15 were synthesized, and their Raman spectra were investigated. La-doping resulted in the enlargement of remnant polarization of Bi4Ti3O12–SrBi4Ti4O15. The structure of the Bi2O2 layers and TiO6 octahedra of the intergrowth was found to be different from those of Bi4Ti3O12 and SrBi4Ti4O15. La3+ ions exhibit pronounced selectivity for the occupation of A site as La content is lower than 0.50, and tend to be incorporated into Bi2O2 layers when the La content is higher than 0.50. Lanthanum substitution brings about the structural phase transition in Bi4Ti3O12–SrBi4Ti4O15. The variation of ferroelectric property may be attributed to combined contribution from the decreasing of the oxygen vacancies, the relaxation of the lattice distortion, the destroying of the insulation and the space charge compensation effects of the Bi2O2 slabs.