• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.256-256
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• 2007

As a candidate for lead-free piezoelectric materials, dense ($(Na_{0.47}K_{0.47}Li_{0.06})NbO_3$ (LNKN6) ceramics were developed by conventional sintering process. Sintering temperature was lowered by adding $Li_2O$ as a sintering aid. Abnormal grain growth in the LNKN6 ceramics was observed with varying $Li_2O$ content. The electrical properties of LNKN6 ceramics were investigated as a function of $Li_2O$ concentration. When the sample sintered at $1000^{\circ}C$ for 4h with the addition of 1 mol% $Li_2O$, electromechanical coupling factor ($k_p$) and piezoelectric coefficient ($d_{33}$) of LNKN6 ceramics were found to reach the highest values of 0.40 and 184 pC/N, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.302-302
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• 2010

The lead-free piezoelectric ceramics must have high piezoelectric properties and electrical properties for the applications of piezoelectric devices. Therefore, KNN ceramics were investigated as a function of the variation of Nb. The density was increased with the increase of Nb. The density was saturated above 0.8895 mol Nb. The maximum value of electromechanical coupling coefficient(kp) was obtained 0.428 at 0.8895mol Nb. This result can be attributed to the well sintered of specimens. Also, The maximum value of mechanical quality factor(Qm) showed 1554 at 0.8895mol Nb. Therefore, this composition can be used for application of piezoelectric device such as piezoelectric transformer and piezoelectric actuator.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.03a
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• pp.12-12
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• 2010

The piezoelecric properties of $(K_{0.5}Na_{0.5})(Nb_{0.96}Sb_{0.04})O_3$+$1.2mol%K_4CuNb_8O_{23}$+$xmol%La_2O_3$ lead-free piezoelecric ceramics were investigated as a function x. These ceramics were fabricated by conventional ceramics processing. Piezoelectric constant ($d_{33}$) and piezoelectric charge coefficient ($g_{33}$) of x=0.2 mol% composition exhibited good properties of 160.3pC/N and 37.4($10^{-3}Vm/N$), respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.7
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• pp.543-546
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• 2011

We studied sintering temperature to enhance the piezoelectric properties of $0.98(Na_{0.5}K_{0.5})NbO_3-0.02Li(Sb_{0.17}Ta_{0.83})O_3$+0.01wt%ZnO (hereafter NKN-LST+ZnO) lead free piezoelectric ceramics. The synthesis and sintering method were the conventional solid state reaction method and sintering was executed at $1,080\sim1,120^{\circ}C$. We found that NKN-LST+ZnO ceramics at optimal sintering temperature showed the improved piezoelectric properties at the optimal sintering temperature. The NKN-LST+ZnO ceramics show good performance with piezoelectric constant $d_{33}$= 153 pC/N sintered at $1,090^{\circ}C$. The results reveal that NKN-LST+ZnO ceramics are promising candidate materials for lead-free piezoelectric application.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.9
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• pp.766-771
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• 2009

Lead-free $0.94(Na_{0.5}K_{0.5})NbO_3$-0.06Ba$(Ti_{0.9}Sn_{0.1})O_3$ [0.94NKN-0.06BTS] ceramics doped with 1 mol% $MnO_2$ were synthesized by a conventional solid state method. The phase transitional behavior and piezoelectric properties of the ceramics sintered at various temperatures were investigated. The 0.94NKN-0.06BTS ceramics sintered at $1050^{\circ}C$, having morphotropic phase boundary of orthorhombic and tetragonal phases, exhibited a microstructure with abnormal grain growth. A diffused phase transition behavior for all the specimens was verified as high degree of diffuseness (${\gamma}$) values from 1.45 to 1.79. A high piezoelectric constant of $d_{33}=256$ pC/N and a satisfactory electromechanical coupling factor of $k_p=42%$ were obtained for the relatively dense 0.94NKN-0.06BTS ceramics sintered at $1050^{\circ}C$.

• 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.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.11
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• pp.2021-2025
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• 2010

Electrical and structural properties were investigated on the effects of ZnO and the lead-free NKN-LST ceramics with the addition of ZnO were fabricated by a conventional mixed oxide method. A gradual change in the crystal and microstructure was observed with the increase of ZnO addition. For the NKN-LST-ZnO ceramics sintered at $1050^{\circ}C$, bulk density increased with the addition of ZnO and showed maximum value at addition 2.0mol% of ZnO. Curie temperature of the NKN-LST-ZnO ceramics slightly decreased with adding ZnO. The dielectric constant, piezoelectric constant ($d_{33}$) and electromechanical coupling factor ($k_p$) increased at the small amount of ZnO addition, which might be due to the increase in density. The high piezoelectric properties = 153 pC/N, electromechanical coupling factor = 0.484 and dielectric constant = 2883 were obtained for the NKN-LST+0.5ZnO ceramics sintered at $1050^{\circ}C$ for 2h.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.7
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• pp.563-567
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• 2011

The most widely used piezoelectric ceramics are lead oxide based ferroelectrics (PZT). However, the toxicity of lead oxide and its high vapor pressure during processing have led to a demand for alternative lead-free piezoelectric materials. We synthesized Lead-free piezoelectric ceramics of $0.96(K_{0.5}Na_{0.5})NbO_3-0.04SrZrO_3+x$ mol% $ZrO_2$ [KNN-SZ+$xZrO_2$; x= 0~0.10] doped with 0.1 wt% $MnO_2$ by a conventional solid state method. We investigated the piezoelectric properties and microstructures of these disk samples sintered in reduced atmosphere in order to evaluate the possibility of the multilayered piezoelectric ceramics having the base metal such as Ni as a internal electrode. All of these KNN-SZ samples sintered in 3%$H_2-97%N_2$ atmosphere at $1,140^{\circ}C$ exhibit pure perovskite structure irrespective of the content of $ZrO_2$. Meanwhile, the sintering denisty and piezoelectric properties such as $K_p$, $Q_m$ and $d_{33}$ of KNN-SZ samples as a function of $ZrO_2$ content show the maxima ($k_p$=28.07%, $Q_m$= 101.34, $d_{33}$= 156 pC/N) at x= 0.04 and it is likely that there is some morphotropic phase boundary(MPB) in this KNN-SZ+$xZrO_2$ composition system. These results indicate that the ceramic composition is a promising candidate material for applications in lead free multilayer piezoelectric ceramics.

• Korean Journal of Materials Research
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• v.26 no.12
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• pp.721-725
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• 2016

This work focuses on the electrical conduction mechanism in a lead free ($Na_{0.5}K_{0.5}NbO_3$ ; NKN) ceramics system with $LiNbO_3$ content of approximately critical concentration $x{\geq}0.2$. Lead free $(1-x)(Na_{0.5}K_{0.5})NbO_3-x(LiNbO_3)$, $NKN-LN_x$ (x = 0.1, 0.2) ceramics were synthesized by solid-state reaction method. Crystal structures are confirmed by X-ray diffraction. The electric-mechanical bond coefficient $k_p$ decreases and the phase transition temperature $T_c$ increases with increasing x content, as determined by dielectric and piezoelectric measurements. The value of the real dielectric constants ${\varepsilon}^{\prime}$ and $k_BT{\varepsilon}^{\prime\prime}$ showed anomalies around $T_c$ ($462^{\circ}C$ in the NKN-LN0.1 and $500^{\circ}C$ in the NKN-LN0.2). For the ionic conduction of mobile ions, the activation energies are obtained as $E_I=1.76eV$ (NKN-LN0.1) and $E_I=1.55eV$ (NKN-LN0.2), above $T_c$, and $E_{II}=0.78$ (NKNL-N0.1) and $E_{II}=0.81$ (NKN-LN0.2) below $T_c$. It is believed that the conduction mechanisms of NKN-LNx ceramics are related to ionic hopping conduction, which may arise mainly due to the jumping of $Li^+$ ions.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.280-280
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• 2007

Lead oxide-based ferroelectrics are the most widely used materials for piezoelectric actuators, sensors and transducers due to their excellent piezoelectric properties. Considering lead toxicity, there is great interest in developing lead-free piezoelectric materials, which are biocompatible and environmentally friendlier. Recently alkali oxide materials, including sodium - potassium niobate (NKN), have been given attention in view of their ultrasonic application and also as promising candidates for piezoelectric lead-free system. However, it is difficult to sinter such NKN-based materials via conventional sintering process. In this reason, many researchers have investigated hot press, hot isostatic press or spark-plasma sintering of NKN-based ceramics. In this study, as candidates for lead-free piezoelectric materials, dense (Na,K,Li)(Nb,Sb)$O_3$ systems were developed by conventional sintering process. The microstructures and piezoelectric properties of the (Na,K,Li)(Nb,Sb)$O_3$ systems were investigated as a function of variable compositions. The excellent piezoelectric and electromechanical properties indicate that this system is potentially good candidate as lead-free material for a wide range of electro-mechanical transducer applications.