Negative Capacitance and Intrinsic Ferroelectric Behavior in α-MoO₃ Culminating as a Robust Piezoelectric Energy Harvester

Driven by the notion that the spectrum of ferroelectric applications can be widened and the current subset of materials could be replaced with earth-abundant, lead-free materials, single-phase α-MoO 3 (MO) with biaxial van der Waals gap was synthesized, revealing an orthorhombic Pmcn symmetry with a layered ABAB... sequence, with mirrored A and B layers. The force-driven dielectric constant of MO was found to be 12.5 at 0.5 N force level, which showed dielectric saturation behavior with increasing dynamic force. Ferroelectric studies revealed a maximum of 46% efficiency at 10 kV/cm external electric field, and piezoelectric modulus ( d 33 ) of 30 pC/N was obtained using the Berlincourt method. Negative capacitance (NC) effects were observed and attributed to the ferroelectric-induced emf and the inductive reactance, in accordance with Lenz’s law. Based on the confluence of the aforementioned features, a piezoelectric energy harvester (PEH) was fabricated, which reached a peak voltage of 4 V under repetitive finger tapping. The power density of the PEH under 100 MΩ resistive load was found to be 7.32 × 10 –1 μW/cm 2 . This enshrines MO as a promising piezoelectric candidate with exotic properties that can be tailored to have multifaceted applications in the realm of sensing and energy harvesting to drive Internet-of-Things and Industry 4.0.