Microstructural modelling of the polarization and properties of porous ferroelectrics

Abstract

Micromechanical models of porous ferroelectric ceramics have often assumed that the material is fully polarised in a particular direction and/or consists of a single isolated pore. In this work the polarisation state in three-dimensional porous polycrystalline ferroelectric networks has been modelled to eradicate the oversimplification of these idealised unit cells. This work reveals that microstructural network models more closely represent a porous ferroelectric microstructure since they are able to take into account the complex polarisation distribution in the material due to the presence of high and low permittivity regions. The modelling approach enables the prediction of the distribution of poled and unpoled material within the structure. The hydrostatic figures of merits and permittivity were determined for a variety of porous lead zirconate titanate microstructures and found to be in good agreement with experimental data. The decrease in piezoelectric activity with porosity was observed to be associated with the complex polarisation state within the material. Model results were shown to be much improved when compared to a model assuming a fully-polarised model.

Manufacture and characterization of porous ferroelectrics for piezoelectric energy harvesting applications

“…The large spread in data is attributed to difficulties in the poling procedure, which is affected by ambient conditions, such as temperature and humidity. The decrease in d 33 in high porosity samples (<40% relative density) may be due to incomplete poling of the BaTiO 3 phase caused by lower breakdown strength that occurs in highly porous dielectric ceramics and complex electric field distribution resulting from a mixture of low and high permittivity phases [7]. Pores are also likely to increase stress concentrations that lead to depolarisation of the material [6] and also limit the grain size in their immediate vicinity, which is thought to inhibit domain motion [8], both of which may reduce the achievable level of polarisation.…”

Understanding the effect of porosity on the polarisation-field response of ferroelectric materials

“…As the decrease in remnant polarisation with porosity level is consistent and relatively clear, the focus is on the coercive field data when contradictory reports of a decreasing or increasing coercive field with increasing porosity are reported. Table 1 and Figure 7(A) summarise the effects of the porosity volume fraction on the Ec value of the porous ferroelectric ceramics from the literature and this work; the data has been separated to those where vp ≲ [20][21][22][23][24][25] vol.% and vp ≳ 20-25 vol.%. It can be seen in Table 1 and Figure 7 that when the porosity volume fraction is low (vp ≲ 20-25 vol.%) the Ec tends to decrease with increasing porosity irrespective of whether the pore morphology is random or aligned.…”

Understanding the peculiarities of the piezoelectric effect in macro-porous BaTiO3

“…Our approach is to ensure the non-poled (i.e. piezo-passive) material surrounding the poled FC inclusion is consistent with model concepts [23] based on the distribution of unpoled and poled regions within the FC material. The FC–air network and modelling were used to interpret the piezoelectric properties and related parameters of porous lead zirconate titanate FCs; however, the shape of poled and unpoled regions was not discussed in detail.…”

“…The FC–air network and modelling were used to interpret the piezoelectric properties and related parameters of porous lead zirconate titanate FCs; however, the shape of poled and unpoled regions was not discussed in detail. [23]…”