Dielectric and piezoelectric properties of porous lead-free 0.5Ba(Ca_0.8Zr_0.2)O₃-0.5(Ba_0.7Ca _0.3)TiO₃ ceramics

Porous barium calcium zirconate titanate 0.5Ba(Ca_0.8Zr_0.2)O₃-0.5(Ba_0.7Ca_0.3)TiO₃ (BCZT) lead-free ferroelectric ceramics were fabricated via a burnt polymer spheres (BURPS) technique by introducing corn starch as the pore-forming agent. The effect of porosity on the microstructure, dielectric, and piezoelectric properties of the porous materials were investigated. An increase in porosity volume fraction from 10% to 25% resulted in an increase in the hydrostatic charge coefficient (d_h), which was 140 to 560% higher than that of the dense BCZT material. An increase in porosity fraction from 10% to 25% also lead to a decrease in relative permittivity that was 16.7% to 60.4% lower than the dense material. These two changes in properties provided a significant enhancement of the hydrostatic figure of merit (d_h∙g_h) for the porous ceramic; for example the d_h∙g_h of the 25 vol.% porous BCZT ceramic was 158 times more than the dense ceramic and demonstrates the potential of porous lead-free ferroelectrics for piezoelectric transducer devices. Reasons for the significant enhancement in piezoelectric performance of the porous ceramics are discussed.