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Bae, Seon-Gi,Shin, Hyea-Gyiung,Sohn, Eun-Young,Im, In-Ho The Korean Institute of Electrical and Electronic 2013 Transactions on Electrical and Electronic Material Vol.14 No.2
$0.95(Na_{0.5}K_{0.5})NbO_3-0.05BaTiO_3+0.2wt%\;Ag_2O$ (hereafter, No excess NKN) ceramics and $0.95(Na_{0.5}K_{0.5})NbO_3-0.05BaTiO_3+0.2wt%\;Ag_2O$ with excess $(Na_{0.5}K_{0.5})NbO_3$ (hereafter, Excess NKN) were fabricated by the conventional solid state sintering method, and their phase transition properties and dielectric properties were investigated. The crystalline structure of No excess NKN ceramics and Excess NKN ceramics were shown characteristics of polymorphic phase transition (hereafter, PPT), especially shift from the orthorhombic to tetragonal phase by increasing sintering temperature range from $1,100^{\circ}C$ to $1,200^{\circ}C$. Also, the temperature coefficient of capacitance (hereafter, TCC) of No excess NKN ceramics and Excess NKN ceramics from $-40^{\circ}C$ to $100^{\circ}C$ was measured to evaluate temperature stability for applications in cold regions. The TCC of No excess NKN and Excess NKN ceramics showed positive TCC characteristics at a temperature range from $-40^{\circ}C$ to $100^{\circ}C$. Especially, Excess NKN showed a smaller TCC gradient than those of Excess NKN ceramics in range from $-40^{\circ}C$ to $100^{\circ}C$. Therefore, NKN piezoelectric ceramics combined with temperature compensated capacitor having negative temperature characteristics is desired for usage in cold regions.
Bae, Seon-Gi,Shin, Hyea-Gyiung,Chung, Kwang-Hyun,Yoo, Ju-Hyun,Im, In-Ho The Korean Institute of Electrical and Electronic 2015 Transactions on Electrical and Electronic Material Vol.16 No.4
The particle sizes of 0.95(K<sub>0.5</sub>Na<sub>0.5</sub>)NbO<sub>3</sub>-0.05BaTiO<sub>3</sub> powder were controlled by secondary milling time after calcination. The average particle sizes, Dmean, of 0.95(K<sub>0.5</sub>Na<sub>0.5</sub>)NbO<sub>3</sub>-0.05BaTiO<sub>3</sub> powders were critically changed from 14.31 μm to 0.91 μm by secondary milling time. The dielectric and piezoelectric properties of 0.95(K<sub>0.5</sub>Na<sub>0.5</sub>)NbO<sub>3</sub>-0.05BaTiO<sub>3</sub> ceramics depended on the particle sizes of powders after calcination and the secondary milling process. As secondary milling times after calcination were increased to more than 48 hr, the dielectric and piezoelectric properties of 0.95(K<sub>0.5</sub>Na<sub>0.5</sub>)NbO<sub>3</sub>-0.05BaTiO<sub>3</sub> ceramics were deteriorated.