Piezoceramic foams made of lead zirconate titanate (PZT) and lithium sodium potassium niobate containing an open porosity >75 vol% are manufactured with varying cell size from 1369 to 265 mm and accordingly, strut size from 346 to 46 mm by replica method. Pore size distribution and strut thickness are determined by X-ray micro tomography investigations of PZT foams with 10, 30, 45, and 80 pores per inch (ppi). Fracture strengths s b between 0.29 and 1.52 MPa (PZT) and 0.04 and 0.07 MPa (LNKN-6) are determined by compression test and compared to Gibson and Ashby's model of open-and closed-cell foams and in dependence of the cell size. The longitudinal and transversal coupling coefficients d 33 and d 31 decrease in a range of 38 to 178 pCN À1 or À13 to À100 pCN À1 compare to dense reference material. In dependence of the cell size, the values of the coupling coefficients change about 79-93%. The relative permittivity decreases 93% by decreasing the cell size of the PZT and LNKN-6 foams.
The small‐signal direct piezoelectric coefficient and dielectric permittivity are characterized as a function of temperature from 25 to 450 °C and uniaxial compressive stress up to 80 MPa in porous Pb(Zr,Ti)O3 (PZT; 10, 20, 30, 40, and 50 vol% porosity). Results show retention of piezoelectric response throughout the temperature range with increasing porosity up to 30 vol%, above which a subsequent decrease is observed. Similarly, increasing porosity did not result in a significant change of the depolarization temperature, although a slight increase in the Curie point is observed with increasing porosity. Macroscopic experimental results are discussed together with microcomputed tomography, which shows the 3D pore structure. These results are important for sensing applications that operate at elevated temperatures and apply compressive stress to the electroactive element.
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