• Korean Journal of Materials Research
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• v.22 no.1
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• pp.35-41
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• 2012

Presently, the most promising family of lead-free piezoelectric ceramics is based on $K_{0.5}Na_{0.5}NbO_3$(KNN). Lithium, silver and antimony co-doped KNN ceramics show high piezoelectric properties at room temperature, but often suffer from abnormal grain growth. In the present work, the $(Ba_{0.85}Ca_{0.15})(Ti_{0.88}Zr_{0.12})O_3$ component, which has relaxor ferroelectric characteristics, was doped to suppress the abnormal grain growth. To investigate this effect, Lead-Free $0.95(K_{0.5}Na_{0.5})_{0.95}Li_{0.05}NbO_3-(0.05-x)AgSbO_3-x(Ba_{0.85}Ca_{0.15})(Ti_{0.88}Zr_{0.12})O_3$[KNLN-AS-xBCTZ] piezoelectric ceramics were synthesized by ball mill and nanosized-milling processes in lead-Free $0.95(K_{0.5}Na_{0.5})_{0.95}Li_{0.05}NbO_3-(0.05-x)AgSbO_3$ in order to suppress the abnormal grain growth. The nanosized milling process of calcined powders enhanced the sintering density. The phase structure, microstructure, and ferroelectric and piezoelectric properties of the KNLN-AS ceramics were systematically investigated. XRD patterns for the doped and undoped samples showed perovskite phase while tetragonality was increased with increasing BCZT content, which increase was closely related to the decrease of TO-T. Dense and uniform microstructures were observed for all of the doped BCZT ceramics. After the addition of BCTZ, the tetragonal-cubic and orthorhombic-tetragonal phase transitions shifted to lower temperatures compared to those for the pure KNNL-AS. A coexistence of the orthorhombic and tetragonal phases was hence formed in the ceramics with x = 0.02 mol at room temperature, leading to a significant enhancement of the piezoelectric properties. For the composition with x = 0.02 mol, the piezoelectric properties showed optimum values of: $d_{33}$ = 185 pC/N, $k_P$ = 41%, $T_C=325^{\circ}C$, $T_{O-T}=-4^{\circ}C$.