Stochastic Polarization Instability in PbTiO_{3}.

Although discussions of structural phase transitions in prototypical ferroelectric systems with the perovskite structure, such as BaTiO_{3} and PbTiO_{3}, started almost seventy years ago, an atomic-level description of the polar characteristics as a function of temperature, pressure, and composition remains topical. Here we provide a novel quantitative description of the temperature-driven local structural correlations in PbTiO_{3} via the development of characteristic relative cationic shifts. The results give new insights into the phase transition beyond those reliant on the long-range order. The ferroelectric-to-paraelectric transition of PbTiO_{3} is realized by the extent of a stochastic polarization instability driven by a progressive misalignment instead of a complete disappearance of the local dipoles, which further suggests that such polarization instability is chemically induced at the morphotropic phase boundary of PbTiO_{3}-based solid solutions with giant piezoelectric effect. As such, our results not only identify the evolving atomistic disorder in a perovskite-based ferroelectric system, but also suggest that polarization instability can serve as a generic fingerprint for phase transitions as well as for better understanding structure-property relationships in PbTiO_{3}-based ferroelectric solid solutions.