This state-of-the-art value outperforms bulk piezoelectric ceramics and composites with randomly dispersed particles, and is comparable to the values reported for the piezoelectric polymers PVDF and P(VDF-TrFE). Optimized composite films are incorporated in flexible piezoelectric touch sensors. The high sensitivity is analyzed and discussed. As the fabrication technology is straightforward and easy to implement, applications are foreseen in flexible electronics such wireless sensor networks and biodiagnostics.

We demonstrate that the figure of merit for materials in piezoelectric energy harvesters does not depend on the compliance.

Vibrational piezoelectric energy harvesters are being investigated to replace batteries in embedded sensor systems. The energy density that can be harvested depends on the figure of merit, d33g33, where d33 and g33 are the piezoelectric charge and voltage coefficient. Commonly used piezoelectric materials are based on inorganic ceramics, such as lead zirconium titanate (PZT), as they exhibit high piezoelectric coefficients. However, ceramics are brittle, leading to mechanical failure under large cyclic strains and, furthermore, PZT is classified as a Substance of Very High Concern (SVHC). To circumvent these drawbacks, we fabricated quasi 1–3 potassium sodium lithium niobate (KNLN) ceramic fibers in a flexible polydimethylsiloxane (PDMS) matrix. The fibers were aligned by dielectrophoresis. We demonstrate for the structured composites values of d33g33 approaching 18 pm3 J−1, comparable to that of state‐of‐the‐art ceramic PZT. This relatively high value is due to the reduced inter‐particle distance in the direction of the electric field. As a confirmation, the stored electrical energy for both material systems was measured under identical mechanical loading conditions. The similar values for KNLN/PDMS and PZT demonstrate that environmentally friendly, lead‐free, mechanically compliant materials can replace state‐of‐the‐art environmentally‐less‐desirable ceramic materials in piezoelectric vibrational energy harvesters.

A high‐voltage coefficient has been found in lead‐free piezoelectric particulate composites based on epoxy with lead‐free (K0.50Na0.50)0.94Li0.06NbO3 (KNLN) piezoceramic particles with a natural cubic morphology. The KNLN powder used in the composites has been prepared using a new solid‐state double calcination processing route. These particles were subsequently used to create random and structured KNLN‐epoxy composites. Using dielectrophoresis, these natural cubical KNLN particles were structured into one‐dimensional chains inside the epoxy matrix. Composites produced with these powders showed piezoelectric properties about a factor of 2 higher than those of composites processed with conventionally calcined KNLN powders. The dielectrophoretically structured KNLN‐epoxy composites with optimized particle size and morphology showed excellent piezoelectric properties, which can replace lead containing piezoelectric composites for sensor and energy harvesting applications in future.