On the Electro-Mechanical Property Characterization of Piezoelectric Inorganic and Hybrid Materials for Energy Harvesting Systems

The energy crisis presents one of the most significant challenges of our century, necessitating the urgent exploration of new methods for electricity generation. A promising approach involves the development of systems made of materials with piezoelectric properties for charge generation and transport. While certain materials such as PZT exhibit excellent piezoelectric properties, the presence of toxic lead hinders their applicability. Consequently, alternative materials such as innovative lanthanide-based tungsten oxide (Ln2WO6), which demonstrate piezoelectric behavior, need to be explored in detail [1-3]. Furthermore, organic materials such as poly(vinyl difluoro ethylene) (PVDF) – based materials possess inherent piezoelectric properties, albeit with weaker coefficients than their inorganic counterparts. However, the addition of piezoelectric nanoparticles like BiFeO3 (BFO) nanoparticles can enhance their piezoelectric response.<br/>This study aims to characterize two distinct types of materials, the inorganic Gd2WO6 oxide in thin film and the hybrid system made of PVDF-b-trifluoro ethylene (PVDF-trFE) block copolymer containing BFO nanoparticles, and subsequently develop a hybrid material that combines the flexibility of the organic component with the structural resistance of the inorganic counterpart, while ensuring piezoelectric sensitivity. To achieve this, we utilized Piezoresponse Force Microscopy (PFM), an Atomic Force Microscopy (AFM) mode based on the inverse piezoelectric effect. Even though the PFM is still universally used to quantify piezo and ferroelectric properties, recent studies have revealed that a significant contribution of the electromechanical response captured by PFM is unfortunately due to artifacts, mostly by electrostatic interactions between the surface and the tip being the most dominant of them [4].<br/>In addition to conventional PFM, another mode has been developed, such as switching spectroscopy PFM (ssPFM). This mode uses a script where the electromechanical response is continuously monitored while alternating between the polarization step and the non-polarization step. The contribution of electrostatic interaction can be minimized by identifying the electrostatic blind spot (ESBS) [5], the laser position on the cantilever that minimizes the electrostatic contribution. This limitation of long-distance electrostatic interaction can be verified through an “almond nut” test. [6] From those data, the ferroelectric hysteresis from the studied material can be extracted.<br/>Through our research, we aim to contribute to the development of piezoelectric hybrid materials with enhanced electromechanical properties. These materials hold significant potential for addressing the energy crisis and driving advancements in electricity generation and utilization.<br/>[1] Carlier, T., et al. ACS Applied Materials & Interfaces (2015) 7(44) 24409-24418<br/>[2] Carlier, T., et al. Materials Chemistry 32(17) (2020) 7188-7200<br/>[3] Lheureux, M., et al. “ACS Applied Electronic Materials (2022) 4(11) 5234-5245<br/>[4] Seol, D.; et al. Current Applied Physics (2017), 17 (5), 661-674.<br/>[5] Killgore, J. P.; et al. Nanoscale Adv. (2022), 4 (8), 2036–2045.<br/>[6] Collins, Let al. ACS Nano (2019), 13 (7), 8055–8066.