A significant improvement of permittivity and energy density will enable the miniaturization of dielectric capacitors and promote integration for applications in electrical power and defense systems. In this work, lamellar composite architectures are fabricated from aligned barium titanate (BaTiO₃) in an epoxy resin using the freeze casting method. Due to the continuous coupling effect originating from the interconnected and highly oriented BaTiO₃ particles, these composites exhibit an extremely high permittivity (ε_r = 1408) at 1 kHz, which is the highest value achieved in BaTiO₃/polymer composites reported so far and fits well to the parallel mode of the mixing rule. A finite element model is used to investigate the local electric field distributions in the BaTiO₃ lamellae under the applied electric field parallel and perpendicular to the freezing direction, respectively. A high ratio value of discharge energy density per electric field, U_dis/E, ∼0.033, is achieved due to a high electric displacement of D = 15.11 μC cm⁻² and a discharge energy density of U_dis = 19.6 × 10⁻² J cm⁻³ is achieved at a low electric field (6 kV mm⁻¹). This work provides an effective strategy of designing a ceramic–polymer composite to realize high permittivity and energy density of capacitors for modern electrical and electronic industries.

Piezoelectrics are an important class of materials for mechanical energy harvesting technologies. In this paper we evaluate the piezoelectric harvesting process and define the key material...

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 . The freeze cast barium titanate with 45 vol.% porosity had a d ₃₃ = 134.5 pC N ⁻¹ compared to d ₃₃ = 144.5 pC N ⁻¹ for dense barium titanate. The d ₃₃ coefficients of the freeze cast materials were also higher than materials with uniformly distributed spherical porosity due to improved poling of the aligned microstructures, as predicted by the models. 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 pm ² N ⁻¹ for barium titanate with 45 vol.% porosity, compared to only 1.40 pm ² 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.