The Research On Processing And Properties In Textured K_0.5Na_0.5NbO₃ Lead-free Piezo-electric Ceramics

A series of lead-based perovskite ceramics, such as PZT, PMN-PT, PZN-PT, show excellent piezoelectric and electromenchanical properties. However, the toxicity of lead oxide and its high vapor pressure during processing have led to a demand for alternative lead-free piezoelectric materials that is a main point in the field of piezoelectric ceramics.This paper has introduced different candidates of lead-free piezoelectric ceramics and development of KNN. Research on fabrication process and properties in textured KNN lead-free piezoelectric ceramics has been shown from three aspects: (1) Tape casting process was designed and confirmed for preparation of textured ceramics. Using mixture of KNbO₃ and NaNbO₃ as ceramics powders, 16.3%vol% slurry was formed by orthogonal test design method, and tape casted to form green sheets, which were cut and laminated to fabricate green compacts. After removal of organic substances from the compacts, the dense KNN ceramics with 98% of TD can be achieved by ordinary sintering in air. (2) Plate-like NaNbO3 particles as template can be synthesized by improved Molten Salt Synthesis, when the content of NaCl as a flux equaled to 8wt% of reactants.(3) Crystalline-Oriented KNN specimens sintered at 1100℃for 1h were found to have densities and pseudo-cubic {100} orientation degrees of 92% and 74% respectively. The disk-shaped specimens were poled at room temperature in a silicon oil under a dc electric of 5 kv/mm for 15min, getting piezoelectric constant d₃₃=117pC/N.Comparing effect of RTGG and TGG methods on fabrication of textured KNN ceramics, high orientation degrees and excellent piezoelectric properties can be achieved by RTGG method. KNN ceramics with 93% of TD were prepared by Microwave-assisted sintering with short thermal treatments. However, it was indicated difficulties for textured ceramics fabricated by Microwave-assisted sintering process.