Enhanced polarization fluctuation in KF-substituted BaTiO3 single crystals

概要

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The longitudinal acoustic (LA) phonon of a Ba088K0.12TiO2.88F0.12 perovskite crystal was investigated through micro-Brillouin scattering measurements to clarify the effect of KF substitution in BaTiO3 on the dynamical properties related to the ferroelectric phase transition. It was found that the LA phonon correlates with the relaxation of dipoles via the piezoelectric coupling inside the polar nanoclusters and that the relaxation has a time scale of 10−13 s; this relaxation is attributed to the hopping of Ti ions in the off-centered sites, even in the high-symmetry cubic phase. Upon KF substitution, the anomalies in the LA phonon become large, indicating that the fluctuation of the order parameter originating from the competition between dipolar forces and thermal agitation is enhanced. We consider that the fluctuation is enhanced by the random electric field induced by the KF substitution.