IoT に給電するグッドバイブレーション (Engineers tap into good vibrations to power the Internet of Things)

Piezoelectric materials convert between mechanical and electrical energy and are a basis for self-powered electronics. Current piezoelectrics exhibit either large charge (d₃₃) or voltage (g₃₃) coefficients but not both simultaneously, and yet the maximum energy density for energy harvesting is determined by the transduction coefficient: d₃₃*g₃₃. In prior piezoelectrics, an increase in polarization usually accompanies a dramatic rise in the dielectric constant, resulting in trade off between d₃₃ and g₃₃. This recognition led us to a design concept: increase polarization through Jahn-Teller lattice distortion and reduce the dielectric constant using a highly confined 0D molecular architecture. With this in mind, we sought to insert a quasi-spherical cation into a Jahn-Teller distorted lattice, increasing the mechanical response for a large piezoelectric coefficient. We implemented this concept by developing EDABCO-CuCl₄ (EDABCO = N-ethyl-1,4-diazoniabicyclo[2.2.2]octonium), a molecular piezoelectric with a d₃₃ of 165 pm/V and g₃₃ of ~2110 × 10⁻³ V m N⁻¹, one that achieved thusly a combined transduction coefficient of 348 × 10⁻¹² m³ J⁻¹. This enables piezoelectric energy harvesting in EDABCO-CuCl₄@PVDF (polyvinylidene fluoride) composite film with a peak power density of 43 µW/cm² (at 50 kPa), the highest value reported for mechanical energy harvesters based on heavy-metal-free molecular piezoelectric.