• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.2
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• pp.116-120
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• 2011

The 0.98 ($Na_{0.44}K_{0.52})Nb_{0.84}O_3-0.02Li_{0.04}$ ($Sb_{0.06}Ta_{0.1})O_3-0.5$ mol%CuO ceramics have been fabircated by ordinary sintering technique and the effect of various calcination method on the electrical propertis and microstructure have been studied. It was observed that the various calcination method influenced the elelctrical properties and structural properties of the 0.98NKN-0.02LST-0.5 mol%CuO ceramics with the optimum piezoelectric constant ($d_{33}$) and electromechanical coupling factor ($k_p$) at room temperature of about $155{\rho}C/N$ and 0.349, respectively, from 0.98NKN-0.02LST-0.5 mol%CuO ceramics sample. The curie temperature ($T_c$) of this ceramic was found at $440^{\circ}C$. The 0.98NKN-0.02LST-0.5 mol%CuO ceramics are a promising lead-free piezoelectric ceramics.

• 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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.32-32
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• 2008

Microstructure and positive temperature coefficient of resistivity (PTCR) characteristics of $0.9BaTiO_3-0.1(Bi_{0.5}Na_{0.5})TiO_3$ [BaBiNT] ceramics doped with $Nb_2O_5$ were investigated in order to develop the Pb-free high Curie temperature ($T_c$)(>$160^{\circ}C$) PTC thermistor. The BaBiNT ceramics showed a tetragonal perovskite structure, irrespective of the added amount of $Nb_2O_5$. They also have a homogeneous microstructure. The resistivity of BaBiNT ceramics was gradually decreased by doping $Nb_2O_5$, which might be due to $Nb^{+5}$ ions substituting for $Ti^{+4}$ sites. The PTCR characteristics of BaBiNT ceramics appeared when the amount of doped $Nb_2O_5$ exceeded 0.0025mol%. Moreover, the abrupt grain growth was observed for the 0.03mol% $Nb_2O_5$added BaBiNT ceramics. It showed an especially high $T_c$ of approximately $172^{\circ}C$ and good PTCR characteristics of a high $\rho_{max}/\rho_{min}$ ratio ($2.96\times10^3$), a high resistivity temperature factor (11.40/$^{\circ}C$) along with a relatively low resistivity ($3.5\times10^4\Omega{\cdot}cm$).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.1
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• pp.29-32
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• 2012

Lead-free $0.98(Na_{0.5},K_{0.5})NbO_3-0.02Li(Sb_{0.17}Ti_{0.83})O_3$ (hereafter 0.98NKN-0.02LST) ceramics doped with $Ag_2O$ were prepared using a conventional mixed oxide method. The specimen showed superior structural and electrical properties when 1 mol% $Ag_2O$ was doped. For the 0.98NKN-0.02LST+1.0mol%$Ag_2O$ ceramics sintered at $1,100^{\circ}C$, piezoelectric constant ($d_{33}$) of sample showed the optimum values of 207 pC/N. The 0.98NKN-0.02LST+1.0 mol%$Ag_2O$ ceramics are a promising candidate for lead-free piezoelectric materials.

• Korean Journal of Materials Research
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• v.29 no.3
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• pp.150-154
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• 2019

This study investigates the effect of MnO2 and CuO as acceptor additives on the microstructure and piezoelectric properties of $0.96(K_{0.5}Na_{0.5})_{0.95}Li_{0.05}Nb_{0.93}Sb_{0.07}O_3-0.04BaZrO_3$, which has a rhombohedral-tetragonal phase boundary composition. $MnO_2$ and CuO-added $0.96(K_{0.5}Na_{0.5})_{0.95}Li_{0.05}Nb_{0.93}Sb_{0.07}O_3-0.04BaZrO_3$ ceramics sintered at a relatively low temperature of $1020^{\circ}C$ show a pure perovskite phase with no secondary phase. As the addition of $MnO_2$ and CuO increases, the sintered density and grain size of the resulting ceramics increases. Due to the difference in the amount of oxygen vacancies produced by B-site substitution, Cu ion doping is more effective for uniform grain growth than Mn ion doping. The formation of oxygen vacancies due to B-site substitution of Cu or Mn ions results in a hardening effect via ferroelectric domain pinning, leading to a reduction in the piezoelectric charge coefficient and improvement of the mechanical quality factor. For the same amount of additive, the addition of CuO is more advantageous for obtaining a high mechanical quality factor than the addition of $MnO_2$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.56-56
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• 2008

최근, 비납 또는 납의 함량을 줄인 압전 세라믹에 대한 관심이 증가하고 있고, 그에 따른 여러 연구가 활발히 이루어지고 있다. 납을 포함하는 세라믹은 높은 소성온도에서 납의 휘발로 인한 특성저하와 환경오염 등이 문제가 된다는 것을 우리는 익히 알고 있다. 그렇기 때문에 PZT계 세라믹스를 대체할 우수한 특성을 가지는 새로운 비납 세리믹스의 조성개발이 시급하다. 비납계 세라믹스 중에서 NKN계를 바탕으로 하는 세라믹스는 가장 기대되는 재료이다. 일반적인 소성에서 순수한 NKN 세라믹은 가장 높은 압전 $d_{33}$상수가 100 pC/N이 넘지 않는다. 그런데 페로브스카이트 구조로된 NKN세라믹스의 A-site에 $Li^{1+}$이온을 치환하면 압전 특성을 향상시킬 수 있다. 그리고, 압전세라믹에서 분극처리는 필수적인데 분극처리는 압전성을 부여할 뿐 아니라 다른 물성도 변화시킴은 잘 알려져 있다. 그러므로 그에 대한 연구 또한 중요한 의미를 갖는다. 따라서 이번 연구에서는 NKN세라믹스에 $Li_2CO_3$를 소결조제로 첨가하여 시편을 제작하였고, 제작된 시편의 특성을 분극전계에 따라 조사하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.95-95
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• 2009

Lead-free $(K_{0.5}Na_{0.5})(Nb_{0.96}Sb_{0.04)O_3$ + 1.2 mol% $K_4CuNb_8O_{23}$ + x mol% $Fe_2O_3$ ceramics were manufactured by a conventional solid state reaction method. And then, their piezoelectric and dielectric properties were investigated. At the 0.2 mol% $Fe_2O_3$ doped ceramics, the values of Kp=0.436 and Qm=696.36 were obtained, respectively, which were suitable for piezoelectric transformer application.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.305-306
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• 2005

In this paper, in order to develop Pb-free piezoelectric ceramics, $(Li_{0.04}Na_{0.44}K_{0.52})(Nb_{0.86}Ta_{0.10}Sb_{0.04})O_3$ ceramics were fabricated with the variation of calcination temperature and sintering temperature. Specimens couldn't be sintered below $111^{\circ}C$ and showed the largest density at calcination temperature of $800^{\circ}C$. Specimens manufactured with the variation of calcination temperature showed pseudo-tetragonal phase, and showed the optimal values of kp=0.45, ${\varepsilon}r$=1336 and $d_{33}$=254 at calcination temperature of $800^{\circ}C$ and sintering temperature of $1110^{\circ}C$.

• 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.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1487-1488
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• 2011

Electrical properties and microstructure were investigated on the effects of $MnO_2$ and the lead-free $(Na_{0.44}K_{0.52}Li_{0.04})(Nb_{0.83}Sb_{0.07}Ta_{0.1})O_3$ ceramics with the addition of $MnO_2$ were fabricated by a conventional mixed oxide method. A gradual change in the crystal and microstructure was observed with the increase of $MnO_2$ addition. For the NKN-LST-xmol%$MnO_2$ sintered at $1100^{\circ}C$, bulk density increased with the addition of $MnO_2$ and showed maximum value at addition 1.0mol% of $MnO_2$. Curie temperature of the NKN-LST ceramics slightly decreased with adding $MnO_2$. The dielectric constant, piezoelectric constant ($d_{33}$) and electromechanical coupling factor ($k_p$) increased below 0.25mol% of $MnO_2$ addition, which might be due to the increase in density. The high piezoelectric properties = 145 pC/N, electromechanical coupling factor = 0.421 and dielectric constant = 2883 were obtained for the NKN-LST-0.25mol%$MnO_2$ sintered at $1100^{\circ}C$ for 4h.