Raman scattering from La-substituted BiFeO3–PbTiO3

Polycrystalline samples of pure BiFeO3–PbTiO3 (BF–PT) and those upon substituting Bi by La up to 50% (x≤0.5) were synthesized using a solid-state reaction method. A composition-driven tetragonal–cubic transition, identified from X-ray diffraction, was found to occur at x=0.4. We report the phonon spectra of pure and La-substituted BF–PT and its assignment. From the behavior of total Raman intensity, the origin of the symmetry-forbidden Raman spectra is identified to lie in substitutional disorder. The dependence of splitting of A1–E modes and that of the LO–TO modes on composition are obtained and their consequences on ionicity are discussed.

Graphical abstractRaman spectrum of the cubic phase (x≥0.4) of La-substituted BF–PT [0.5(Bi1−xLaxFeO3)0.5(PbTiO3)] consists of 7 modes, while group theory does not predict any Raman active phonon.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Composition-driven tetragonal–cubic transition in La-substituted BF–PT. ► Phonon spectra in the tetragonal phase assigned. ► A1–E anisotropy splitting of phonons decreases upon La-substitution. ► Increase in LO–TO splitting at larger La composition due to higher ionicity.