Thickness-confined metastable phase transitions drive large piezoelectricity in ultrathin BiFeO 3

作者：Shuang-Jie Chen, Meixiong Zhu, Jing-Hui Wang, T. F. Shi, Jiaqi Liu, Yujia Wang, Yinlian Zhu, Xiu-Liang Ma, Zuhuang Chen, Yun‐Long Tang · 发表于：Science Advances · 年份：2026 · DOI：10.1126/sciadv.aeb7174 · 研究领域：Multiferroics and related materials、Ferroelectric and Piezoelectric Materials、Advanced Sensor and Energy Harvesting Materials

Pursuing high-performance lead-free piezoelectrics beyond classical thickness limits remains challenging. This study identifies a transitional phase between rhombohedral and tetragonal structures in strained ultrathin BiFeO 3 layers within (BiFeO 3 /Ca 0.96 Ce 0.04 MnO 3 ) 4 multilayer films grown on LaAlO 3 substrates. Atom-scale studies and quantitative electromechanical atomic force microscopy revealed that the transitional phase facilitates continuous polarization rotation in ultrathin BiFeO 3 layers. This effect enhances the piezoelectric responses of the multilayer films and yields a giant piezoelectric coefficient ( d 33 ≈ 30 picometers per volt) for films containing 16–unit cell BiFeO 3 layers, which is over four times higher than conventional rhombohedral BiFeO 3 . Phase-field simulations confirmed a thickness-dependent electromechanical coupling regularity, behaving as the coexistence of transitional/tetragonal mixed phases and dense nanodomains in strained ultrathin BiFeO 3 layers. This work breaks the thickness limit of single-layer BiFeO 3 for electromechanical applications and proposes a thickness-domain design strategy for lead-free piezoelectric heterostructures.