Phonons in La-Substituted BiFeO3-PbTiO3

(Bi(1-x)La(x))(0.5)Pb(0..5)Fe(0.5)Ti(0.5)O(3) (BF-PT) ceramics were prepared for x = 0.0, 0.2, 0.3, 0.4 and 0.5 using solid state reaction method. x = 0.0 samples were found to have tetragonal perovskite structure, same as that of PbTiO(3) (PT), while in La-substituted samples tetragonal distortion reduced and system turned cubic at 40 % La-concentration. Raman spectroscopic investigations reveal 10 modes in pure BF-PT which were assigned by comparing with those in PT. Although in the cubic phase no Raman active phonons are expected, 7 modes are found that have correspondence with those of the tetragonal phase. The modes in the cubic phase are activated due to substitutional disorder at cation site.