Microstructures, dielectric and piezoelectric properties of unannealed and annealed porous 0.36BiScO₃-0.64PbTiO₃ ceramics

Porous 0.36BiScO₃–0.64PbTiO₃ (BS–0.64PT) ceramics were fabricated with poly methyl methacrylate microsphere (PMMA, φ18 μm) as pore forming agent. When PMMA contents increased from 10 to 60 vol%, the porosity increased from 9.4 to 43.9 %. X-ray diffraction analysis indicated that all porous ceramics were well crystallized with pure perovskite phase. As the porosity increased, the grain size decreased gradually. Correspondingly the piezoelectric coefficient (d ₃₃) decreased from 397 to 290 pC/N, and acoustic impedance (Z) decreased gradually from 14.64 to 5.08 × 10⁶ kg/m² s. The dielectric constant (ε _r) at room temperature decreased rapidly from 1284 to 405. Moreover, the Curie temperature (T _c) decreases from 428 to 415 °C, which was attributed to the accelerated reversal of domain in the boundary of pores. After annealing process, d ₃₃ were improved significantly, in the range of 415 to 390 pC/N. The dielectric properties, domains, and polarization were observed to discuss the annealing effects on the electrical properties. In summary, annealing process improved the piezoelectric properties of porous BS–0.64PT ceramics effectively, promising for applications piezoelectric transducer for high-temperature application (>200 °C).