• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.7
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• pp.506-510
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• 2012

In this study, lead-free $(Na_{0.465}K_{0.465}Bi_{0.07})(Nb_{0.93}Ti_{0.07})O_3-0.08MnO_2$ ceramics were fabricated by conventional mixed oxide method. Structural and electrical properties of lead-free $(Na_{0.465}K_{0.465}Bi_{0.07})(Nb_{0.93}Ti_{0.07})O_3-0.08MnO_2$ ceramics with the variation of sintering temperature were investigated. As results of x-ray diffraction analysis, all specimens showed a typical polycrystalline perovskite structure without presence of the second phase. Sintered density increased with an increases of sintering temperature and the specimen sintered at $1,020^{\circ}C$ showed the maximum value of 4.5 $g/cm^3$. The average grain size of the $(Na_{0.465}K_{0.465}Bi_{0.07})(Nb_{0.93}Ti_{0.07})O_3-0.08MnO_2$ specimen sintered at $1,020^{\circ}C$ is about 0.83 ${\mu}m$. Electromechanical coupling factor, relative dielectric constant and dielectric loss of $(Na_{0.465}K_{0.465}Bi_{0.07})(Nb_{0.93}Ti_{0.07})O_3-0.08MnO_2$ specimens sintered at $1,020^{\circ}C$ were 0.252, 741 and 0.043% respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.2
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• pp.104-108
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• 2013

In this paper, the $0.95(Na_{0.5}K_{0.5})_{0.04}[(Nb_{0.8}Ta_{0.20})_{0.994}Co_{0.015}]O_3$(abbreviated as NKNT) + $0.05KNbO_3$ lead-free piezoelectric ceramics were synthesized by the conventional mixed oxide method route with normal sintering. And also, the effects of calcination temperature on the microstructure, dielectric properties, and piezoelectric properties were investigated. A polymorphic phase transition(PPT) between orthorhombic and tetragonal phases was observed in specimens calcined at $810^{\circ}C{\sim}850^{\circ}C$. The ceramics calcined at $830^{\circ}C$ showed excellent piezoelectric properties: $d_{33}$= 179 pC/N, $k_p$= 0.384, $Q_m$= 79.73). These results indicate that the ceramic is a promising candidate material for lead-free piezoelectric ceramics.

• Journal of Sensor Science and Technology
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• v.19 no.2
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• pp.155-159
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• 2010

0.96$(Na_{0.5}K_{0.5})NbO_3$-0.04$(Ba_{(1-x)}Sr_x)TiO_3$ lead free piezoelectric ceramics were synthesized to enhance the piezoelectric properties of (Na,K)$NbO_3$. The systhesis and sintering method were the conventional solid state reaction method and general sintering method in air atmosphere. The polymorphic phase transition(PPT) was observed at all composition(0 $\leq$ x $\leq$ 0.05) when $(Ba_{(1-x)}Sr_x)TiO_3$ were added in the $(Na_{0.5}K_{0.5})NbO_3$. As Sr concentration was increased, grain size, dielectric loss(tan$\delta$) and mechanical quality factor($Q_m$) were decreased and piezoelectric constant($d_{33}$) and electromechanical coupling factor($k_p$) were increased within a limited value. The optimized piezoelectric and properties, $d_{33}$, $k_p$, $Q_m$, and tand, of 0.96$(Na_{0.5}K_{0.5})NbO_3$-0.04$(Ba_{(1-x)}Sr_x)TiO_3$ were 139 pC/N, 0.31 %, 95, 0.04 at the composition of x=0.04.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.5
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• pp.355-359
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• 2013

In this paper, the $0.995(Li_{0.04}(Na_{0.56}K_{0.44})_{0.96}(Nb_{0.90}Ta_{0.10})_{0.998}Zn_{0.005}O_3+0.005KNbO_3+xwt%\;TeO_2$ lead-free piezoelectric ceramics for energy harvesting devices were fabricated by the conventional mixed oxide method. The microstructure, dielectric, and piezoelectric properties were investigated as a function of the $TeO_2$ addition. All the specimens showed an orthorhombic phase structure. At the composition ceramics doped with 0.1 wt%$TeO_2$, the optimum values of $d_{33}$= 212 pC/N, $d_{33}{\cdot}g_{33}=9.54pm^2/N$, and kp=0.448 were obtained, respectively. The results indicate that the composition ceramics is a promising candidate for energy harvesting devices applications.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.8
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• pp.622-626
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• 2011

Lead-free piezoelectric ceramics with the composition of $(Na_{0.54}K_{0.46})_{0.96}Li_{0.04}(Nb_{1-0.10-x}Ta_{0.10}Sb_x)O_{3}$ (x= 0~8 mol%) were fabricated by nomal sintering at $1,090^{\circ}C$ for 5 h. the phase structure, microstructure and electrical properties were investigated with a emphasis on the influence of the Sb content. All samples exhibit a single perovskite phase over the whole compositional range. For the ceramics with x= 4 [mol%], two phase transitions are observed at $75^{\circ}C$ and $366^{\circ}C$, corresponding to the phase transitions of orthorhombic to tetragonal (To-t) and tetragonal to cubic (Tc), respectively. high electrical properties of $d_{33}$= 210.83 pC/N, kp= 40%, ${\varepsilon}_r$= 1,091.35, $\rho$= 4.54 g/$cm^2$ were obtained from the specimen with x= 4 [mol%], which suggests that the composition ceramics is a promising lead-free piezoelectric material.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.3
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• pp.204-208
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• 2013

In this study, $KNbO_3$-substituted (Li,Na,K)(Nb,Sb,Ta)$O_3$ ceramics were investigated to develop Pb-free composition ceramics for multilayer actuator and energy harvester applications. The X-ray diffraction analysis indicated that all samples were pure perovskite phase and no secondary phase was found. A tetragonality as a function of $KNbO_3$ substitution showed the maximum value at 1.5 mol% $KNbO_3$ and then decreased. The SEM image analysis showed the maximum grain size of $3.14{\mu}m$ at 1.5mol% $KNbO_3$. In the composition ceramics with 1.5 mol% $KNbO_3$ sintered at $1,100^{\circ}C$, excellent properties of density= 4.75 $g/cm^3$, electromechanical coupling factor ($k_p$)= 0.50 and piezoelectric constant($d_{33}$)= 290 pC/N were obtained, respectively, suitable for piezoelectric actuator and energy harvester applications.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.6
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• pp.489-494
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• 2009

In this study, In order to improve dielectric and piezoelectric properties of Lead-free piezoelectric ceramics, $0.95(K_{0.5}Na_{0.5})NbO_3-0.05Li(Sb_{0.8}Nb_{0.2})O_3+0.2\;wt%Ag_2O+0.4\;wt%MnO_2+Xwt%CuO$ were investigated as a function of the amount of CuO addition. With increasing the amount of CuO addition, density was increased up to 0.4 wt.% CuO and then decreased above. And also, electro mechanical coupling factor ($k_p$) was decreased. At the 0.4 wt% CuO added specimen sintered at $1020^{\circ}C$, $k_p$, Qm, density, dielectric constant (${\varepsilon}_r$) and $d_{33}$[pC/N] showed the optimal value of $4.37\;g/cm^3$, 0.354, 305, 645, and 144 pC/N respectively.