UNEXPECTED TEMPERATURE-DEPENDENCE OF FERROIC DOMAIN DYNAMICS AND STABILITY

Ferroelectrics are functional materials that exhibit unique collective behavior of ions and electrons. Most ferroelectric crystals exhibit also ferroelasticity, i.e. elastic domains that contribute to a stress-strain hysteretic loop. Several competing models have been developed to describe the domain dynamics, stability and origin, including the Landau-Ginzburg-Devonshire theory as well as models that associate the domain dynamics with creep. A major difference between these models is the temperature dependence of the ferroic domains as a function of temperature. Yet, to-date, the experimental data related to the temperature dependence of the domains is lacking, mainly due to experimental challenges related to imaging the domain behavior while varying the temperature, hence hindering our fundamental understanding of the unique collective electron and ion behavior in ferroics.

Here, we showed the behavior of submicron ferroic domains as a function of temperature, by means of direct observation. Specifically, we demonstrated that upon heating, the coercive field required to switch a ferroelectric 180° domain in thin PZT films is increasing, unexpectedly. Likewise, by imaging the ferroelastic domain dynamics during the orthorhombic-tetragonal phase transition in single-crystal BaTiO₃, we illustrated that ferroelastic domains release mechanical strain in mechanisms that are reminiscence of soft-matter mechanics: wrinkling, and doubling. These unique strain release mechanisms allowed us to better understand the electro-mechanical coupling in ferroelectrics at the domain scale and hence the origin of collective behavior in these materials.