Spark Plasma Sintering of Tungsten Bronze Sr_(2-x)Ca_xNaNb_5O_(15) (x= 0.1) Piezoelectric Ceramics: Ⅱ, Electrical Properties

摘要

Sr_(2-x)Ca_xNaNb_5O_(15) (SCNN, x = 0.1) piezoelectric ceramics with tetragonal tungsten bonze structure were successfully produced by spark plasma sintering. Part Ⅰ of this study presented the sintering of these highly dense ceramics. The current work investigates their electrical (dielectric, ferroelectric, and piezoelectric) properties and relates them to the sintering parameters (temperature, heating rate, and soaking time) and crystallographic orientation. The results show that the electrical properties of SCNN are enhanced with increasing heating rate and soaking time. Dielectric study reveals a less pronounced diffuse phase transition of SCNN. Anisotropic electrical properties were observed as a result of the preferred crystallographic orientation in the sintered ceramics. The samples sintered at 1200℃ for 30 min exhibited the highest electrical properties, and showed the following piezoelectric properties when poled across the direction perpendicular to the pressing direction: electromechanical planar and thickness coupling coefficients of κ_p = 9.5% and κ_t = 39.6%, and piezoelectric constant of d_(33) = 121 pC/N (～45% of the single-crystal value).