Mechanical energy is one of the most widespread ambient energies that can be captured and converted into electrical energy. Piezoelectric devices such as resonant cantilevers are thus widely investigated for vibration energy harvesting, due to the simplicity of electromechanical conversion. The production of green electricity from the environment is attractive and is leading to the development of small and autonomous electronic devices powered by piezoelectric energy. However, high performance piezoelectric materials (electromechanical coupling factor and piezoelectric coefficient) are required, and particular attention must be paid to energy-efficient manufacturing processes in order to remain in line with the green deal. Drastically reducing the processing temperature of ceramics is also a scientific challenge, given the current trend to increase the flexibility of piezoelectric nanogenerators. Indeed, this implies the use of nanomaterials and polymers to design stretchable generators for wearable or Internet of Things applications. Recent advances and developments in this context will be discussed. Then, the low-temperature elaboration of two technologically important piezoelectrics: Pb(Zr,Ti)O3 (PZT) and (K,Na)NbO3 (KNN) will be presented. The replacement of PZT has stimulated research into lead-free piezoelectrics, but the environmental merits of PZT and KNN are still debated. Both contain critical and highly volatile metal elements, which is a major problem during high-temperature processing. The combination of spark plasma sintering and screen-printing technology offers several advantages, in particular a reduction in the number of processing steps and a lower overall thermal budget. First, proof-of-concept based on PZT devices will be illustrated. Then, we will focus on lead-free piezoelectric ceramics KNN, highlighting different strategies for drastically reducing sintering temperatures. In the MEMS manufacturing perspective, the co-sintering of flexible substrate/metal electrode/piezoelectric ceramic multilayers requires the control of chemistry, interfaces and microstructure. In terms of properties, the emphasis is on dielectric and piezoelectric properties, which are sensitive to microstructure and defect chemistry.

Antiferroelectric materials possess exceptional functional properties at the field-induced antipolar to polar transition that enable high-efficiency energy storage, high-strain/high-force actuators, and solid-state cooling. PbZrO₃ is the prototypical antiferroelectric, and PbZrO₃-based thin films have been studied extensively for energy storage applications where combinations of paraelectric-like behavior at low fields and a ferroelectric response at high fields promise both high efficiency and high energy storage densities. However, processing phase-pure perovskite PbZrO₃ thin films is challenging due to large Pb loss at the processing temperatures, resulting in the formation of deleterious secondary phases. Pb loss in perovskites is normally compensated by providing Pb excess with respect to the stoichiometry (in the target or precursor solution), or by PbO deposition beneath, between, or on top of the perovskite films of interest. Here we investigate the effects of different Pb loss compensation strategies on chemical solution processed PbZrO₃ thin films of ~200 nm in thickness. Specifically, we consider: 1) excess Pb with respect to stoichiometry in the 2MOE-based precursor solution; 2) PbO seed layers; and 3) PbO capping layers. PbO seed layers were deposited before the first PbZrO₃ films directly on the substrate, while “capping” layers were deposited after the final layer of PbZrO₃ was crystallized. X-ray diffraction showed strong crystallographic orientation (>90%) – with 001-oriented films obtained using seed layers and 042-oriented ones without seed layers – and no signature of secondary phases. However, high-resolution energy dispersive x-ray spectroscopy in TEM often revealed local Pb-deficient volumes and Pb-rich nanocrystals at crystallization interfaces. Nanocrystals were also observed by SEM on film surfaces, but their presence diminished using PbO capping layer. 001-oriented films exhibited higher forward and return transitions fields (~640 and 410 kV/cm, respectively) than their 042 counterparts (~350 and ~220 kV/cm, respectively). The 001-oriented films exhibited breakdown strengths up to 1450 kV/cm with a recoverable energy storage density of 14 J/cm³ and 70% efficiency at this field. 042-oriented films showed breakdown strengths up to 945 kV/cm with recoverable energy storage density of up to 12 J/cm³ and 54% efficiency before breakdown.

This study focuses on a cost-efficient and adaptable approach for synthesizing a Flexible Hybrid Nanogenerator (FHNG). The composite, which comprises lead-free piezoelectric Ba0.92Ca0.08Zr0.10Ti0.90O3 (BCZT) and Zinc Oxide (ZnO), was synthesized through the reflux method. Fabrication of the FHNG involved incorporating BCZT/ZnO as a reinforcement within the polydimethylsiloxane (PDMS) matrix using a dispersion method. X-Ray Diffraction (XRD) analysis unveiled the presence of tetragonal and rhombohedral phases of BCZT, as well as the hexagonal phase of ZnO, and also confirmed the successful synthesis of the nanocomposite (BCZT/ZnO) at room temperature. A comprehensive exploration of dielectric, ferroelectric, and optical properties ensued. The notable increase in dielectric constant at lower frequencies was attributed to the space charge polarization phenomenon. Remnant polarization (Pr) achieved 0.326 µC/cm2 on the application of a 160 kV/cm electric field. The peak open-circuit voltage (VOC) and short-circuit current (ISC) of FHNG were scrutinized on various mechanical stresses from 10 Pa to 450 Pa, exhibiting maximum VOC ≈ 6.2 V and ISC ≈ 90 nA. This technology, exemplifying practicality and adaptability, lays the foundation for prospective applications in flexible electronics, encompassing wearable devices, electronic skin, the Internet of Things (IoT) network, and environmental monitoring systems.