Distortion of Inversion Symmetry in Biaxial Van der Waals Layered Oxide Leading to Negative Capacitance (NC) Effect and Intrinsic Ferroelectricity

Piezoelectric materials find applications in a diverse array of devices, such as sensors, resonators, motors, actuators, high-resolution ultrasound devices, and microscopic filters for cellular communications. The synthesis of single-phase α-MoO₃ (MO) with a biaxial van der Waals (vdW) gap revealed orthorhombic <i>Pmcn</i> symmetry featuring a layered ABAB sequence with mirrored A and B layers. Applying a force magnitude of 0.5 N unveiled a force-driven dielectric constant of 12.5 in MO, showcasing distinctive dielectric saturation behavior. Ferroelectric investigations, conducted with a 10 kV/cm external electric field, demonstrated an efficiency peak of 46%, while the Berlincourt technique yielded a piezoelectric modulus (d₃₃) of 30 pC/N. Negative capacitance (NC) effects, correlated with inductive reactance and ferroelectric-induced emf per Lenz's law, were observed. Combining these characteristics, a piezoelectric energy harvester (PEH) was engineered, achieving a peak voltage of 4 V under repeated finger tapping. When subjected to a resistive load of 100 MΩ, the PEH exhibited a power density of 7.32 x 10^-1 μW/cm². These findings position α-MoO₃ as an exceptional piezoelectric candidate in the realms of sensing and energy harvesting, contributing to the advancement of the Internet of Things (IoT) and Industry 4.0.