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. 2026 Mar 2;65(10):e9911471.
doi: 10.1002/anie.9911471. Epub 2026 Jan 27.

Surface Ferroelectricity in Lead-Free Nonferroelectric Chiral Perovskites Beyond Neumann's Principle

Zhi Yang  1 , Yunlong Bai  1 , Jiandong Yao  1 , Yangding Qiu  1 , Qihang Deng  1 , Jie Wu  1 , Guankui Long  2 , Bingsuo Zou  3 , Jia Hong Pan  3 , Ruosheng Zeng  1
Affiliations

Surface Ferroelectricity in Lead-Free Nonferroelectric Chiral Perovskites Beyond Neumann's Principle

Zhi Yang et al. Angew Chem Int Ed Engl. .

Abstract

According to Neumann's Principle, the chiral-polar photovoltaic effect (CPPE) is restricted to crystals in one of the five chiral ferroelectric space groups-based on the assumption of perfect long-range periodicity and bulk symmetry. However, this framework overlooks symmetry breaking at crystal boundaries. Herein, we report the emergence of surface ferroelectricity in a one-dimensional chiral nonferroelectric perovskite, R/S-MPZSbBr5 (MPZ = 2-methylpiperazine), achieved through interlayer antiparallel alignment of polar Sb-Br chains. The bulk structure adopts a nonferroelectric phase with alternating polar domains, resulting in net-zero polarization. Yet, at the (001) surface, the breaking of continuous translational symmetry gives rise to local ferroelectricity. This surface-driven polarization, coupled with the intrinsic chirality of the crystal, enables a localized CPPE. Moreover, the synergy between surface ferroelectricity and pyro-photovoltaic effects significantly enhances the performance of self-powered circularly polarized light (CPL) detection. Our work reveals the limitations of Neumann's Principle at crystal interfaces and opens new avenues for engineering ferroelectricity and chiral optoelectronics in nonferroelectric systems.

Keywords: Neumann's Principle; circularly polarized light photodetector; ferroelectricity; perovskites; symmetry breaking.

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