Raman scattering study of La-, Nd- and Sm-substituted Bi4Ti3O12

Raman modes of bismuth-layered perovskite Bi4-xLaxTi3O12 ceramic samples were studied as a function of La content from x = 0.00 to 0.75. In the low-wavenumber region ( 35 similar to 150 cm(-1)), the rigid mode was found to be insensitive to La substitution, while the compositional change caused a frequency upshift of one of the soft modes. In the high-wavenumber region, the results indicated that a structure transition from orthorhombic to tetragonal may occur above x = 0.75, since the B-2g and B-3g modes showed evidence of coalescence into E-g modes with increasing La content. Raman spectra of Bi3.25Nd0.75Ti3O12 and Bi3.25Sm0.75Ti3O12 are presented and compared with Bi4-xLaxTi3O12.