Uniting Ferroelectricity, Piezoelectricity, and Axial Negative Thermal Expansion in Single-Component Organic Materials Enables High-Performance Memristor and Energy-Harvesting Nanogenerators.

Abstract

The development of ferroelectric materials is fundamentally constrained by the stringent requirement for crystallization within polar space groups. Moreover, integrating multiple functionalities, such as ferroelectricity, piezoelectricity, and negative thermal expansion (NTE), into a single-component organic material remains a significant challenge, despite the demand for sustainable, wearable, high-precision electronics. In this study, we report a symmetry-breaking strategy to transform para-halogenated 3-oxo-2-phenylhydrazineyline indolines from centrosymmetric to polar space groups via controlled oxidation. The novel isostructural oxo-derivatives exhibit robust ferroelectricity (P_s and E_c ranging from 1.3 to 6.3 µC.cm^-2 and 4 to 9.6 kV.cm^-1, respectively), supported by quantum-mechanical calculations. Detailed crystal structure analysis reveals the mechanisms governing their polarization and ferroelectric domain switching. Leveraging its superior polarization, the chloro-analog-based device demonstrated high-performance memristive behavior with stable bipolar resistive switching at minimal bias (∼1 V). The piezoelectric nanogenerators demonstrated superior energy-harvesting capabilities, including rapid charging and high power density (up to 4.23 µW.cm^-2). Additionally, bromo- and iodo-analogs experienced moderate to colossal axial NTE, and all three analogs displayed minimal volumetric expansion. This study represents the first demonstration of single-component organic materials that unite ferroelectric, piezoelectric, and NTE properties, providing a blueprint for multifunctional, high-precision micro- and nanoelectronics.