Effect of poling direction and porosity on piezoelectric figures of merit: A numerical study

Piezoelectric materials are at front of scientific research when it comes to sensing, actuation and energy harvesting from smart materials and structures. Crucial to such materials is their output power and performance in terms of figure of merit (FOM). In the present paper, we have compared the effect of two approaches, namely, introducing porosity and poling tuning on different figures of merit. Here, two material systems, 0.3BaTiO₃-0.7NaNbO₃ (BT-NNb) and Pb[Zr_xTi_1-x]O₃ (PZT-5A), have been considered and the effective piezoelectric properties for different porosity levels (upto 25% volume fraction) and at different poling orientations were computed using representative volume element (RVE). It was observed that for BT-NNb the effective properties get optimised at a given poling orientation unlike in PZT-5A. For BT-NNb, without poling tuning, the maximum change in FOM₃₁, FOM₃₃ and FOM_h (associated with transverse (d₃₁), longitudinal (d₃₃) and hydrostatic (d_h) piezoelectric strain coefficients) was found to be 14.3%, 14.1% and 14.4% for 25% porous (by volume) system. On the other hand, for the same system, at optimum poling orientation all the FOMs were found to be ∼ 1000 times higher than their corresponding initial values. However, in PZT-5A, no optimum poling orientation was observed and thus it was concluded that FOMs can only be improved by introducing porosity in the system.