Porous Structure Enhances the Longitudinal Piezoelectric Coefficient and Electromechanical Coupling Coefficient of Lead‐Free (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃

The introduction of porosity into ferroelectric ceramics can decrease the effective permittivity, thereby enhancing the open circuit voltage and electrical energy generated by the direct piezoelectric effect. However, the decrease in the longitudinal piezoelectric coefficient (d₃₃) with increasing porosity levels currently limiting the range of pore fractions that can be employed. By introducing aligned lamellar pores into (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃, this paper demonstrates an unusual 22-41% enhancement in the d₃₃ compared to its dense counterpart. This unique combination of high d₃₃ and a low permittivity leads to a significantly improved voltage coefficient (g₃₃), energy harvesting figure of merit (FoM₃₃) and electromechanical coupling coefficient ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msubsup><mml:mi>k</mml:mi> <mml:mn>33</mml:mn> <mml:mn>2</mml:mn></mml:msubsup> <mml:annotation>$k_{33}^2$</mml:annotation></mml:semantics> </mml:math> ). The underlying mechanism for the improved properties is demonstrated to be a synergy between the low defect concentration and high internal polarizing field within the porous lamellar structure. This work provides insights into the design of porous ferroelectrics for applications related to sensors, energy harvesters, and actuators.