Lead-free BaTiO3-based porous ceramics with the enhanced piezoelectric figure of merit for energy harvesting applications
CIOMAGA C. 1, HORCHIDAN N. 1, DUMITRU I. 1,2, TUFESCU F. 1
1 Department of Exact and Natural Sciences, Institute of Interdisciplinary Research, Alexandru Ioan Cuza University of Iasi, Carol I, 700506, Iasi, Romania, Iasi, Romania; 2 Faculty of Physics, Alexandru Ioan Cuza University Iasi, Carol I, 700506, Iasi, Romania, Iasi, Romania
Due to their excellent electromechanical conversion properties, piezoelectric materials have attracted growing attention for energy harvesting applications. The present study focuses on the preparation of a Pb-free material with high piezoelectricity that possesses a combination of physical (figures of merit (FOM)) properties. The challenge in obtaining piezoelectric materials with enhanced FOM is to reduce the dielectric constant while keeping the piezoelectric performances high. Recent studies demonstrated the benefits of introducing porosity in ceramics for various purposes and improving piezoelectric FOM for energy harvesting applications. To increase the piezoelectric performances, solid solutions of BaTiO3 close to the morphotropic phase boundary like in Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCTZ), were proposed. Porous BCTZ ceramics have been fabricated via the burn polymer spheres technique using poly(methyl methacrylate) (PMMA) microspheres as a sacrificial template. The low dielectric properties have been studied for the obtained BCTZ ceramics with various porosity levels (from 4 to 30% of porosity). The dielectric constant as a function of frequency indicates a gradual reduction of dielectric with increasing porosity as a result of the “dilution effect” due to the air pores. Using mechanical stimuli at different frequencies, the obtained materials have been tested for their piezoelectric energy harvesting capabilities. The piezoelectric measurements have shown that the piezoelectric response increases with increasing porosity level while the permittivity decreases, requirements necessary as a material to present enhanced piezoelectric energy harvesting figures of merit (FOM). The experimental set-up realized for measuring and testing the piezoelectric response has demonstrated and confirmed the beneficial effect of porosity for the collected signal over a specific frequency range with high interest for energy conversion as f = 10 ÷ 500 Hz. In conclusion, we have obtained porous BCTZ ceramics for which the permittivity decreases and piezoelectric FOM increases, requirements important for considering them as materials for energy harvesting applications.
Acknowledgment: This work was supported by a grant of the Romanian Ministry of Education and Research, CNCS – UEFISCDI, project no PN-III-P4-ID-PCE-2020-1988, within PNCDI III.