Microscopic origins of the large piezoelectricity of lead-free (Ba,Ca)(Zr,Ti)O₃

In light of directives around the world to eliminate toxic materials in various technologies, finding lead-free materials with high piezoelectric responses is an important current scientific quest. The recent discovery of a large electromechanical conversion near room temperature in (1 − x)Ba(Zr_0.2Ti_0.8)O₃–x(Ba_0.7Ca_0.3)TiO₃ compounds has attracted a lot of attention. Strikingly, the origin of such a strongly desired response is not conclusively understood.

Here, we report the development of a large-scale atomistic scheme providing a microscopic insight into this technologically-promising material. The use of such a scheme reveals that high piezoelectricity in this material originates from the existence of large fluctuations of the polarization in the orthorhombic state arising from the combination of flat free-energy surfaces, a fragmented local structure, and the narrow temperature window around room temperature at which this orthorhombic phase is the equilibrium state.

Nature Communications 8, 15944 (2017)