Publikationsdatum:
2014-10-22
Beschreibung:
A (K,Na)NbO 3 -based lead-free piezoelectric ceramic was successfully densified. It exhibited an enhanced electromechanical coupling factor of k p = 0.52, a piezoelectric constant d 33 = 252 pC/N, and a frequency constant N p = 3170 Hz m because of the incorporation of an elaborate secondary phase composed primarily of KTiNbO 5 . The ceramic's nominal composition was 0.92K 0.42 Na 0.44 Ca 0.04 Li 0.02 Nb 0.85 O 3 –0.047K 0.85 Ti 0.85 Nb 1.15 O 5 –0.023BaZrO 3 –0.0017Co 3 O 4 –0.002Fe 2 O 3 –0.005ZnO, abbreviated herein as KNN–NTK composite. The KNN–NTK ceramic exhibited a dense microstructure with few microvoids which significantly degraded its piezoelectric properties. Elemental maps recorded using transmission electron microscopy with energy-dispersive X-ray spectroscopy (TEM–EDS) revealed regions of high concentrations of Co and Zn inside the NTK phase. In addition, X-ray diffraction patterns confirmed that a small portion of the NTK phase was converted into K 2 (Ti,Nb,Co,Zn) 6 O 13 or CoZnTiO 4 by a possible reaction between Co and Zn solutes and the NTK phase during a programmed sintering schedule. TEM studies also clarified a distortion around the KNN/NTK interfaces. Such an NTK phase filled voids between KNN particles, resulting in an improved chemical stability of the KNN ceramic. The manufacturing process was subsequently scaled to 100 kg per batch for granulated ceramic powder using a spray-drying technique. The properties of the KNN–NTK composite ceramic produced using the scaled-up method were confirmed to be identical to those of the ceramic prepared by conventional solid-state reaction sintering. Consequently, slight changes in the NTK phase composition and the distortion around the KNN/NTK interfaces affected the KNN–NTK composite ceramic's piezoelectric characteristics.
Print ISSN:
0021-8979
Digitale ISSN:
1089-7550
Thema:
Physik
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