17 research outputs found
Freeze cast porous barium titanate for enhanced piezoelectric energy harvesting
Energy harvesting is an important developing technology for a new generation
of self-powered sensor networks. This paper demonstrates the significant
improvement in the piezoelectric energy harvesting performance of barium
titanate by forming highly aligned porosity using freeze casting. Firstly, a
finite element model demonstrating the effect of pore morphology and angle with
respect to poling field on the poling behaviour of porous ferroelectrics was
developed. A second model was then developed to understand the influence of
microstructure-property relationships on the poling behaviour of porous freeze
cast ferroelectric materials and their resultant piezoelectric and energy
harvesting properties. To compare with model predictions, porous barium
titanate was fabricated using freeze casting to form highly aligned
microstructures with excellent longitudinal piezoelectric strain coefficients,
d 33. Both model and experimental data indicated that introducing porosity
provides a large reduction in the permittivity () of barium titanate, which
leads to a substantial increase in energy harvesting figure of merit, , with a
maximum of 3.79 pm2 N-1 for barium titanate with 45 vol.% porosity, compared to
only 1.40 pm2 N-1 for dense barium titanate. Dense and porous barium titanate
materials were then used to harvest energy from a mechanical excitation by
rectification and storage of the piezoelectric charge on a capacitor. The
porous barium titanate charged the capacitor to a voltage of 234 mV compared to
96 mV for the dense material, indicating a 2.4-fold increase that was similar
to that predicted by the energy harvesting figures of merit
Porous ferroelectrics for energy harvesting applications
This paper provides an overview of energy harvesting using ferroelectric materials, with a particular focus on the energy harvesting capabilities of porous ferroelectric ceramics for both piezo- and pyroelectric harvesting. The benefits of introducing porosity into ferro- electrics such as lead zirconate titanate (PZT) has been known for over 30 years, but the potential advantages for energy harvesting from both ambient vibrations and temperature fluctuations have not been studied in depth. The article briefly discusses piezoelectric and pyro- electric energy harvesting, before evaluating the potential benefits of porous materials for increasing energy harvesting figures of merits and electromechanical/electrothermal coupling factors. Established processing routes are evaluated in terms of the final porous structure and the resulting effects on the electrical, thermal and mechanical properties