Raman scattering study of La-doped SrBi2Nb2O9 ceramics

La doped SrBi2Nb2O9 ( LSBN) ferroelectric ceramics prepared by the solid-state reaction technique exhibit composition-dependent remanent polarization. X-ray diffraction ( XRD) and Raman scattering have been carried out to investigate the effects of La doping on the crystal structure of SrBi2Nb2O9 ( SBN). The XRD study shows that the ceramics exhibit increasing preferred c orientation with increasing La content. The results of Raman scattering reveal that the doping La3+ ions prefer to replace Sr2+ in the A sites of the perovskite blocks ( SrNb2O7) at a low doping content and they may also occupy the Bi3+ sites in the Bi2O2 layers with further increasing La content. Accordingly, the observed variation of the ferroelectric properties with the La content in LSBN ceramics can be attributed to the competitive results of La substitution in A sites and Bi3+ sites. Our results demonstrate that the ferroelectric properties of La doped SBN are strongly related to the occupied sites of La3+ ions.