Mechanical Anisotropy in a One-Dimensional Hybrid Perovskite Ferroelectric with Giant Piezoelectric Response

Organic–inorganic hybrid perovskites (OIHPs) have garnered significant attention due to their broad application prospects in energy storage, photovoltaics, and electronics. Their mechanical properties, which are crucial for optimizing device processing techniques and ensuring long-term operational reliability, have been extensively investigated in three-dimensional (3D) OIHPs such as CH₃NH₃PbX₃ (X = I, Br, Cl) and two-dimensional (2D) lead halide OIHPs. However, the mechanical properties of one-dimensional (1D) OIHPs remain largely unexplored. Herein, we have investigated the mechanical anisotropy of a 1D OIHP ferroelectric, TMCM–CdCl₃, known for its large piezoelectric coefficient, by both density functional theory (DFT) calculations and nanoindentation characterizations. It exhibits pronounced mechanical anisotropy on different crystallographic planes of (001), (020), and (110), including an elastic modulus (E) ratio of 1.40:1.13:1.00 and a hardness (H) ratio of 1.00:2.06:1.65 experimentally, which mainly originates from the 1D chain configuration. Interestingly, the contradiction between DFT and nanoindentation results has been revealed to be closely linked to the distinct pile-up phenomena. Moreover, the onset stress of elastic–plastic deformation has been unveiled to be 191–276 MPa, which is essential for practical piezoelectric applications. This work reveals the pronounced mechanical anisotropy and involved mechanisms in the 1D OIHP TMCM–CdCl₃ and provides guidance for design and fabrication of hybrid piezoelectric-based devices.