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High-pressure Raman study of a relaxor ferroelectric: The Na 0.5 Bi 0.5 TiO </mml:…

2001; American Physical Society; Volume: 63; Issue: 17 Linguagem: Inglês

10.1103/physrevb.63.174106

1095-3795

J. Kreisel, A. M. Glazer, Pierre Bouvier, G. Lucazeau,

Microwave Dielectric Ceramics Synthesis

We report high-pressure Raman measurements (up to 19 GPa) on the perovskite-type relaxor ferroelectric sodium-bismuth-titanate, ${\mathrm{Na}}_{0.5}{\mathrm{Bi}}_{0.5}{\mathrm{TiO}}_{3}$ (NBT). Distinct changes in the Raman spectra have been analyzed in the light of a rhombohedral-to-orthorhombic $(R3c\ensuremath{-}\mathrm{t}\mathrm{o}\ensuremath{-}\mathit{Pnma})$ phase transition. Results show that this transition, involving a change in the tilt system and the cation displacement, does not occur in a single step, but goes through an intermediate phase (2.7 to 5 GPa). The frequency evolution of characteristic bands in the Raman spectra allows us to propose a scenario where in the early stage of the transition a change in the A-cation displacement $([111{]}_{p}\ensuremath{\rightarrow}[010{]}_{p})$ takes place, while at least one other change, i.e., B-site cation displacement $([111{]}_{p}\ensuremath{\rightarrow}[000])$ or the tilt change ${(a}^{\ensuremath{-}}{a}^{\ensuremath{-}}{a}^{\ensuremath{-}}\ensuremath{\rightarrow}{a}^{\ensuremath{-}}{b}^{+}{a}^{\ensuremath{-}}),$ appears to happen only at higher pressures. A pressure-induced breakdown of the Raman intensity, preceding the phase transition, has been observed for the bands at 135 and 275 ${\mathrm{cm}}^{\ensuremath{-}1}.$ It is suggested that a change in the polar character of nanosized ${\mathrm{Bi}}^{3+}{\mathrm{TiO}}_{3}$ and ${\mathrm{Na}}^{1+}{\mathrm{TiO}}_{3}$ clusters is at the origin of this observation, being, in fact, the signature of a pressure-induced relaxor-to-antiferroelectric crossover in NBT. Raman spectroscopy is shown to be an effective technique to investigate the pressure-dependent behavior in relaxor ferroelectrics.