High Piezoelectric Voltage Coefficient in Structured Lead‐Free (K,Na,Li)NbO₃ Particulate—Epoxy Composites

Abstract

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.

Flexible Piezoelectric Touch Sensor by Alignment of Lead‐Free Alkaline Niobate Microcubes in PDMS

“…composites. This value is more than one order of magnitude higher than that obtained for randomly dispersed particle composites [17][18][19][20][21][22][23][24][25][26][31][32][33][34][35] and on par with the values reported for the piezoelectric polymers PVDF and P(VDF-TrFE). [14][15][16] The explanation for the increase in g 33 is that d 33 strongly depends on the intra-chain connectivity, while ε r is a bulk property, proportional to the fill factor but almost independent of the microstructure.…”

“…[22][23][24] Aligned composite films have been reported with piezoelectric voltage coefficients attaining 120 mV m N -1 . [25,26] The Curie temperature remains, in first order approximation, that of the ceramic filler. The main drawback of these composites is that the voltage coefficient lags behind that of PVDF and of P(VDF-TrFE).…”

Flexible Lead‐Free Piezoelectric Composite Materials for Energy Harvesting Applications

“…The optimal conditions obtained were an electric field of 15 kV/mm, a temperature of 150°C and a poling time of 5 minutes. [21,24,25,31] Meanwhile, in all cases the dielectric loss does not exceed 3 %, and slightly increases with alignment. We note that the conditions used for poling are in perfect agreement with reported poling studies on comparable KNLN/PDMS composites.…”

“…[21,24,25] The process is schematically depicted in Figure 2b. [21,24,25] The process is schematically depicted in Figure 2b.…”

“…More importantly however, the charge coefficient strongly depends on the connectivity, defined as the number of dimensions in which a phase is selfconnected. [21,24,25] Contrary to the charge coefficient, the dielectric constant, ɛ r , experiences only a marginal increase due to alignment of the particles. In this convention, the first digit refers to the active piezoelectric ceramic phase, while the second digit refers to the polymeric matrix.…”