Fabrication of porous PZT-PZN piezoelectric ceramics with high hydrostatic figure of merits using camphene-based freeze casting

Porous lead zirconate titanate-lead zinc niobate (PZT-PZN) piezoelectric ceramics with interconnected pore channels were fabricated using the camphene-based freeze-casting method. In this method, warm PZT-PZN/camphene slurries with various solid loadings (10, 15, 20, and 25 vol%) were prepared by ball milling at 60°C and then cast into molds at 20°C, resulting in the formation of solidified green bodies comprised of three-dimensionally interconnected camphene dendrite networks and concentrated ceramic particle walls. After the removal of the frozen camphene via sublimation, the samples were sintered at 1200°C for 2 h. All of the fabricated samples showed highly porous structures, consisting of fully dense PZT-PZN walls without defects, such as cracks or pores. As the initial solid loading was decreased from 25 to 10 vol%, the porosity was linearly increased from 50% to 82%. This increase in the porosity led to a reduction in the permittivity, a moderate decline in the d₃₃ value, and a rapid decline in the d₃₁ value, which endowed the porous samples with a high hydrostatic figure of merit (HFOM). The highest HFOM value of 35650 × 10^-15 Pa^-1 was achieved for the sample with a porosity of 82%, as well as ε₃₃= 284, d_h=298 pC/N, and g_h=118 × 10^-3 V·(m·Pa)^-1.