Observation of nonequilibrium behavior near the Lifshitzpoint in ferroelectrics with incommensurate phase

Abstract

We have investigated nonequilibrium properties of proper uniaxial Sn2P2(SexS1−x )6 ferroelectrics with the type II incommensurate phase above Lifshitz point xLP ∼ 0.28.We performed measurements of dielectric susceptibility in cooling and heating regimes with the rate ranging 0.002–0.1 K/min, as well as high-resolution ultrasound investigation and hypersound Brillouin scattering experiments. For samples with x ! 0.28 clear anomalies are observed at incommensurate second-order transition (Ti) and at first-order lock-in transition (Tc) in the regime of very slow cooling rate, whereas the intermediate incommensurate phase is not observed when the rate is faster than 0.1 K/min. In general, increasing the cooling rate leads to smearing of the anomaly at Tc. We relate this effect to cooling rate dependence of domain-wall concentration and their size: domain width decreases when cooling rate increases. At certain conditions, the size of domain is comparable to the incommensurate phase modulation period, which is in the micrometer range in the vicinity of Lifshitz point and leads to pinning of the modulation period by domain walls.