Origin of Disorder Tolerance in Piezoelectric Materials and Design of Polar Systems

Current
high-performing piezoelectric materials are dominated by
perovskites that rely on soft optical phonon modes stabilized by disorder
near a morphotropic phase boundary and a unique resilience of the
polar response to that disorder. To identify structural families with
similar resilience, we develop a first-principles sensitivity analysis
approach to determine the effect of disorder on the piezoelectric
response for structures in the Materials Project database. In well-known
piezoelectric systems, the lattice dynamics, rather than internal
strain or dielectric, control the polar response. Additionally, multiple
stable optical phonon modes are found to contribute to the piezoelectric
response, providing a fingerprint for disorder tolerance. A multiple-phonon
mode criterion is used to evaluate candidate materials for disorder-tolerant
piezoelectric prototype systems. Five promising structures are altered
through chemical substitution, generating potential MPB end points
with large piezoelectric responses beyond perovskites including Akermanite
Sr2xCa2 – 2xCoSi2O7, which exhibits a nearly 20%
increase in response at the 50% composition.

当前高性能压电材料多以钙钛矿为主体，这类材料依赖于由无序效应稳定的软光学声子模，该无序效应存在于准同型相界（morphotropic phase boundary, MPB）附近，且其极化响应对该无序效应具备独特的抗扰能力。为识别具备类似抗扰能力的结构族系，我们开发了一种第一性原理灵敏度分析方法，用于定量分析无序效应对材料项目（Materials Project）数据库中各类结构压电响应的影响。在已被广泛研究的压电体系中，调控极化响应的核心因素是晶格动力学，而非内应变或介电性能。此外，研究发现多个稳定的光学声子模可共同参与压电响应的调控，这一现象可作为抗无序能力的特征标识。我们采用多声子模准则，对抗无序压电原型体系的候选材料进行筛选评估。通过化学取代对五种具有应用潜力的结构进行改性，得到了一系列具备大压电响应、性能超越钙钛矿体系的潜在MPB端点相，其中镁黄长石（Akermanite）Sr₂ₓCa_{2-2x}CoSi₂O₇在组分占比为50%时，其压电响应提升近20%。