Microscopic origins of the large piezoelectricity of leadfree (Ba,Ca)(Zr,Ti)O3

Abstract

In light of directives around the world to eliminate toxic materials in various technologies, finding lead-free materials with high piezoelectric responses constitutes an important current scientific goal. As such, the recent discovery of a large electromechanical conversion near room temperature in (1−x)Ba(Zr0.2Ti0.8)O3−x(Ba0.7Ca0.3)TiO3 compounds has directed attention to understanding its origin. Here, we report the development of a large-scale atomistic scheme providing a microscopic insight into this technologically promising material. We find that its high piezoelectricity originates from the existence of large fluctuations of polarization in the orthorhombic state arising from the combination of a flat free-energy landscape, a fragmented local structure, and the narrow temperature window around room temperature at which this orthorhombic phase is the equilibrium state. In addition to deepening the current knowledge on piezoelectricity, these findings have the potential to guide the design of other lead-free materials with large electromechanical responses.

Single crystal growth of BaZrO3 from the melt at 2700 °C using optical floating zone technique and growth prospects from BaB2O4 flux at 1350 °C

“…More particularly, BaZrO 3 is known to be used in lead-free BaTiO 3 -based (BCTZ) [25] solid solutions which exhibits high piezoelectric response [26], whereby its role in the polarization mechanisms at the phase convergence region of this system remains poorly understood [27]. For a better understanding of the remarkable piezoelectric response of BCTZ solid solution, it is of great importance to measure the intrinsic properties [24] of BaZrO 3 single crystals in order to comprehend and to model more accurately BaTiO 3 -CaTiO 3 -BaZrO 3 phase diagram as previously reported [28][29][30].…”

Phenomenological modeling of phase transitions and electrocaloric effect in Ba(Zr0.2Ti0.8)O3‐(Ba0.7Ca0.3)TiO3

“…As mentioned in the Theory section, some approximation and assumption were made as well. In fact, as suggested by Heitmann et al the Curie‐Weiss constant might well be composition dependent, plus there is also controversy about the phase convergence region …”

“…Figure presents the computed composition‐temperature phase diagram for BZT‐ x BCT using two sets of free energy coefficients derived in the present study (see Table ). Data points from previous experiments [1‐2, 5, 7, 9, and 17] and first‐principles calculations are also shown for comparison. It is clear that our computation fits the experiments fairly well [1‐2, 5, 7, 9, and 17] over a wide composition or temperature range.…”

“… and first‐principles calculations Ref. are shown for comparison [Color figure can be viewed at wileyonlinelibrary.com]…”

“…The origin of high piezoelectricity has been explored based on experimental and theoretical studies, which suggest that perhaps several mechanisms work together to achieve the observed high performance. The following mechanisms have been proposed as origin for high piezoelectricity: flat‐free energy profile at the tricritical point, low polarization anisotropy energy, low energy barrier at the O‐T phase boundary, and large polarization fluctuation in the O phase . Heitmann and Rossetti proposed a Landau‐Ginzburg‐Devonshire (LGD) phenomenological model and computed composition‐temperature phase diagram for a number of solid solution systems including BZT‐ x BCT.…”