SUBSTITUTION SITE OF LANTHANUM IONS IN LA-DOPED SrBi 4 Ti 4 O 15 and Bi 4 Ti 3 O 12 -SrBi 4 Ti 4 O 15.

Ferroelectric ceramics of lanthanum-modified SrBi 4 Ti 4 O 15 and Bi 4 Ti 3 O 12 -SrBi 4 Ti 4 O 15 have been synthesized, and Raman spectrum measurements have been carried out at room temperature. The investigation on the Raman spectra 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 Bi 2 O 2 layers in the La-doped SrBi 4 Ti 4 O 15 . As for La-doped Bi 4 Ti 3 O 12 -SrBi 4 Ti 4 O 15 , the critical content of the doping ions is 0.50. An interesting phenomenon has been noticed that the remnant polarization maximized at about the critical doping content. Thus, it can be concluded that the Bi 2 O 2 layers have a very important effect on the properties in the bismuth layer-structured ferroelectric materials. [ABSTRACT FROM AUTHOR]