Piezoelectric and structural properties of bismuth sodium potassium titanate lead-free ceramics for energy harvesting

The development of bulk piezoelectric ceramics with high energy conversion efficiency is of decisive importance for the requirements of the advanced energy harvesting devices toward miniaturization and integration. There is an additional motivation in the piezoelectric ceramics, lead titanate-zirconate (PZT) ceramics are the most widely used energy harvesting (EH) materials. This fact is important because legal restrictions on the use of lead in electronic devices have led to greater efforts being made to develop lead-free alternatives to PZT-based materials. Here, we propose the Bi0.5(Na0.8K0.2)0.5TiO3 (BNKT) lead-free piezoceramics as a good candidate for the replacement of toxic lead compounds for energy harvesting applications. For that, we have carried out a systematic study of the voltage generation of BNKT-based piezoceramics for (EH) purposes. Specifically, our results reveal that the BNKT–based lead-free piezoceramics show adequated effective capacitance and output energy due to more effective performance with a piezoelectric charge coefficient and a maximum generated output voltage as high as 12.8 pC/N and 19.9 V, respectively. Finally, we consider that the design of new lead-free piezoceramics with superior property coefficients and functionalities, such as the BNKT-based piezoceramics, should be seriously considered as candidates for the replacement of the current toxic lead-based compounds.

Frequency Invariability of (Pb,La)(Zr,Ti)O3 Antiferroelectric Thick-Film Micro-Cantilevers

Micro-electromechanical systems comprising antiferroelectric layers can offer both actuation and transduction to integrated technologies. Micro-cantilevers based on the (Pb0.97La0.02)(Zr0.95Ti0.05)O3 (PLZT) antiferroelectric thick film are fabricated by the micro-nano manufacturing process, to utilize the effect of phase transition induced strain and sharp phase switch of antiferroelectric materials. When micro-cantilevers made of antiferroelectric thick films were driven by sweep voltages, there were two resonant peaks corresponding to the natural frequency shift from 27.8 to 27.0 kHz, before and after phase transition. This is the compensation principle for the PLZT micro-cantilever to tune the natural frequency by the amplitude modulation of driving voltage, rather than of frequency modulation. Considering the natural frequency shift about 0.8 kHz and the frequency tuning ability about 156 Hz/V before the phase transition, this can compensate the frequency shift caused by increasing temperature by tuning only the amplitude of driving voltage, when the ultrasonic micro-transducer made of antiferroelectric thick films works for such a long period. Therefore, antiferroelectric thick films with hetero-structures incorporated into PLZT micro-cantilevers not only require a lower driving voltage (no more than 40 V) than rival bulk piezoelectric ceramics, but also exhibit better performance of frequency invariability, based on the amplitude modulation.