High-resolution Brillouin scattering studies of phase transitions and precursor phenomena in PbZr0.78Sn0.22O3 single crystals

Brillouin scattering study of phase transitions in antiferroelectric PbZr0.78Sn0.22O3 (PZS) single crystals were performed in the temperature range 300-1173 K. The frequency of longitudinal acoustic (LA) mode begins to exhibit a strong decrease below about 950 K, followed by an increase in the line-width below about 700 K. The line-width (frequency) exhibits a maximum (minimum) at Tc1 = 482 K, the phase transition from the paraelectric (PE) phase to an intermediate, antiferroelectric phase (AFE2). In addition, a broad central peak (CP) appears, indicating presence of polar nanoclusters in the PE phase. This CP exhibits critical slowing down upon approaching Tc1 from above, indicating a significant contribution of an order-disorder mechanism to the PE-AFE2 phase transition. Present Brillouin study gives strong evidence that upon cooling dynamical clusters appear already near 950 K. Upon further cooling, PZS exhibits other acoustic anomalies at 462 K. These step-like anomalies indicate onset of the phase transition from the AFE2 phase into another antiferroelectric phase (AFE1). This phase transition is not accompanied by any singularity in CP intensity and critical slowing down of the relaxation time, suggesting a displacive nature of this transition.