Crystal structure evolution and local symmetry of perovskite solid solution Ba[(Fe1/2Nb1/2)1-xTix]O3 investigated by Raman spectra

The local crystal structure and phonon modes of Ba[(Fe1/2Nb1/2)(1-x)Ti-x]O-3 solid solutions (x = 0, 0.2, 0.4, 0.6, 0.8, 0.85, 0.9, 0.95) were investigated by Raman spectroscopy in the range of 100-1000 cm(-1) at room temperature. Typical tetragonal structure with C-4v symmetry was determined for Ba[(Fe1/2Nb1/2)(0.05)Ti-0.95]O-3, which was in accordance with the X-ray diffraction (XRD) result. Similar Raman spectra with broader peaks were observed for x decreasing from 0.95 to 0.80, indicating weakening of the Ti4+ displacement. New features in low-, medium- and high-wavenumber regions were observed in Raman spectra of Ba[(Fe1/2Nb1/2)(1-x)Ti-x]O-3 system with x <= 0.6, which could be attributed to the heterogeneous distribution of multiple B-site ions. Most interestingly, two-mode-like behavior was observed in the high-wavenumber region in Raman spectra of Ba(Fe1/2Nb1/2)O-3 and Ba[(Fe1/2Nb1/2)(0.8)Ti-0.2]O-3, which was probably caused by very local chemically heterogeneous zones of NbO6 and FeO6. As the existence of the local Nb rich region, slight distortion of octahedron could be expected due to the second-order Jahn-Teller (SOJT) effect of Nb5+ ion. The local composition fluctuation could play an important role in the unique relaxor-like dielectric characteristics of Ba(Fe1/2Nb1/2)O-3. (C) 2011 American Institute of Physics. [doi:10.1063/1.3639283]