Orienting anisometric pores in ferroelectrics: Piezoelectric property engineering through local electric field distributions

Abstract

Ferroelectrics are a technologically important class of materials, used in actuators, sensors, transducers, and memory devices. Introducing porosity into these materials offers a method of tuning functional properties for certain applications, such as piezoand pyroelectric sensors and energy harvesters. However, the effect of porosity on the polarization switching behaviour of ferroelectrics, which is the fundamental physical process determining their functional properties, remains poorly understood. In part, this is due to the complex effects of porous structure on the local electric field distributions within these materials. To this end, freeze cast porous lead zirconate titanate ceramics were fabricated with highly oriented, anisometric pores and an overall porosity of 34 vol.%. Samples were sectioned at different angles relative to the freezing direction and the effect of pore angle on the switching behaviour was tracked by simultaneously measuring the temporal polarization and strain responses of the materials to high voltage pulses. Finite element modelling was used to assess the effect of the pore structure on the local electric field distributions within the material, providing insight into the experimental observations. It is shown that increasing the pore angle relative to the applied electric field direction decreases the local electric field, resulting in a reduced domain wall dynamic and a broadening of the distribution of switching times. Excellent longitudinal piezoelectric (d33 = 630 pm/V) and strain responses (Sbip = 0.25% and Sneg = 0.13%, respectively), comparable to the dense material (d33 = 648 pm/V, Sbip = 0.31% and Sneg = 0.16%), were found in the PZT with anisometric pores aligned with the poling axis. Orienting the pores perpendicular to the poling axis resulted in the largest reductions in the 2 effective permittivity (𝜀 33 𝜎 = 200 compared to 𝜀 33 𝜎 = 4100 for the dense at 1 kHz), yielding the highest piezoelectric voltage coefficient (g33 = 216 x 10 -3 Vm/N) and energy harvesting figure of merit (d33g33 = 73 x 10 -12 m 2 /N). These results demonstrate that a wide range of application-specific properties can be achieved by careful control of the porous microstructure. This work provides a new understanding of the interplay between the local electric field distribution and polarization reversal in porous ferroelectrics, which is an important step towards further improving the properties of this promising class of materials for sensing, energy harvesting, and low-force actuators.

Porous ferroelectric materials for energy technologies: current status and future perspectives

“…45 In their next work, series-connected with respect to the freezing direction were prepared. They found that the remnant polarization decreased with an increase in orientation angle, 127 which was related to the local electric field distribution within the porous microstructure, which on average both broadens and reduces in magnitude with increasing pore orientation angle. From the previous studies, it can be concluded that porous ferroelectric ceramics with parallelconnected structure had the highest remnant polarization.…”

“…However, the blocking force would also be reduced compared to dense materials due to the lower stiffness of porous ferroelectrics, so they may be more suitable for low-force actuation applications. 127 For acoustic projector applications, Butler derived a projector-transducer figure of merit (FoMv)…”

Domain wall-grain boundary interactions in polycrystalline Pb(Zr0.7Ti0.3)O3 piezoceramics

“…Ferroelectric ceramics are widely applicable in electronic devices and are indispensable in actuators, high-dielectric-constant capacitors, piezoelectric sensors, and ultrasonic transducers [1][2][3]. Microstructural and crystallographic parameters, such as crystal structure [4], degree of crystallographic texture [5,6], lattice distortion [7], and porosity [8] are commonly used to tailor their application-relevant electrical and electromechanical properties. Grain-size engineering is one of the most important tools and was previously used to tailor properties, such as permittivity [9], strain [10], fracture toughness [11], polarization reversal [12], electrical fatigue [13], high-power piezoelectric properties [14], and even phase transitions [15].…”

Mechanical Manipulation of Nano‐Twinned Ferroelectric Domain Structures for Multilevel Data Storage

“…Furthermore, the average d 33 of the PbZr 0.2 Ti 0.8 O 3 thin film obtained from the PFM amplitude loops (recorded at a frequency away from resonance), is ≈40 pm V −1 , indicating that the tip loading force could induce a piezoelectric field of 2.5 MV cm −1 . In principle, the piezoelectric field has an opposite direction to the original polarization direction, because the piezoelectric coefficient has opposite signs for different polarization states, [ 48 ] while the flexoelectric field always points from the surface of the film toward the substrate. When the high tip pressure is applied to the film with the downward polarization, the internal electric fields induced by the flexoelectric and the piezoelectric effects point to the opposite directions, however, the piezoelectric electric field is much stronger than the flexoelectric field and the negative coercive field.…”

“…The observed upward switching of domains can be attributed to the combined effects of the built-in electric field and the mechanical force. [41][42][43]47] It was reported that both piezoelectric effect and flexoelectric effect can be induced by the strain and the strain gradient imposed by the tip, [48][49][50][51][52] and they could induce an internal electric field in the film. When a loading force of 3051.8 nN is applied to the film by a PFM tip with a radius of 25 nm, it will induce a high pressure of ≈1.5 GPa.…”