• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.30-30
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• 2008

Lead-free piezoelectric ceramics 0.97$(Na_{0.5}K_{0.5})NbO_3$-0.03Ba$(Ti_{1-x}Sn_x)O_3$ [NKN-BTS-x] ceramics doped with 1 mol% $MnO_2$ have been fabricated by a sintering technique with muffling. The $MnO_2$-doped NKN-BTS-x ceramics with x$\leq$0.2 have pure orthorhombic perovskite structure at room temperature. The dense microstructure was developed with grain growth as an increase of amount of Sn. Moreover, the addition of Sn was found to have a significant influence on piezoelectric properties. In particular, the $MnO_2$-doped NKN-BTS-0.1 ceramics showed improved piezoelectric properties of piezoelectric constant ($d_{33}$=145pC/N), relatively large electromechanical coupling factor ($k_p$=43%), dielectic constant (${\varepsilon}^T_{33}/{\varepsilon}_0$=676) dielectric loss (tan$\delta$=1.3%).

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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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 ($3.5\times10^4\Omega{\cdot}cm$).

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 하계학술대회 논문집
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• pp.324-324
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• 2010

최근에는 압전체의 환경오염 문제의 해결 및 가격경쟁력을 갖추기 위해서 비납계 압전체에 대한 연구가 활발히 진행되고 있다. (Na,K)$NbO_3$ 계는 페로브스카이트 구조를 가지는 비납계 세라믹스로 현재 가장 많이 연구되고 있는 물질 중의 하나이다. 본 연구에서는 압전성이 우수한 $(Na_{0.44}K_{0.52}Li_{0.04})(Nb_{0.9}Ta_{0.04}Sb_{0.06})O_3$ 조성에 CuO, $Cu_2O$ 등의 Cu 산화물을 첨가하였을 때의 전기기계결합계수, 기계적품질계수, 비유전율, 압전전하상수, 문극-전계 이력곡선 (P-E hysteresis curve) 등을 변화를 평가하고자 하였다.

• 한국전기전자재료학회논문지
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• 제25권3호
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• pp.198-203
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• 2012

In this study, $[Li_{0.04}(Na_{0.5}K_{0.5})_{0.96}](Nb_{0.86}Ta_{0.10}Sb_{0.04})O_3+xSrO$ (x=0, 0.0025, 0.005, 0.0075) ceramics were synthesized by the conventional mixed oxide method. The X-ray diffraction patterns demonstrated that ceramics possessed single perovskite structure. The SEM images indicate that microstructure can be obviously affected by a small amount of added SrO. The phase transition temperature tetragonal-cubic($T_c$) and orthorhombic-tetragonal($T_{o-t}$) shifts downward and upward with the increase of Sr addition, respectively. The excellent piezoelectric properties of $d_{33}=170[pC/N]$, $k_p=0.37$, $Q_m=64.12$, $T_{o-t}=153^{\circ}C$ and $T_c=370^{\circ}C$ were obtained from the 0.25 mol% Sr added ceramics sintered at $1,120^{\circ}C$ for 1 h.

• Transactions on Electrical and Electronic Materials
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• 제11권3호
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• pp.126-129
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• 2010

(1-X) $(Na_{0.5}K_{0.5})NbO_3-X$ $K_4CuNb_8O_{23}$ (NKN-X KCN) ceramics were produced using the conventional solid state sintering method, and their sinterability and electric properties were investigated. The density, dielectric constant (${\varepsilon}_r$), piezoelectric constant $d_{33}$, electromechanical coupling factor $k_p$ and mechanical quality factor $Q_m$ value of the NKN ceramics depended upon the KCN content and the sintering temperature. In particular, the KCN addition to the NKN greatly improved the mechanical quality factor $Q_m$ value. The ceramic with X = 2.0 mol% sintered at $1,150^{\circ}C$ possesses the optimum properties (${\varepsilon}_r=241$, $d_{33}=78$, $k_p=0.34$ and $Q_m=1,121$). These results indicate that the ceramic is a promising candidate material for applications in lead free piezoelectric transformer and filter materials.

• 한국전기전자재료학회논문지
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• 제26권11호
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• pp.806-809
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• 2013

In this study, $(Na_{0.525}K_{0.443}Li_{0.037})(Nb_{0.883}Sb_{0.08}Ta_{0.037})O_3+0.10\;wt%Bi_2O_3+0.35\;wt%B_2O_3$ ceramics were prepared by conventional soild-state sintering process. The specimens were sintered at temperature range from $1,060^{\circ}C$ to $1,100^{\circ}C$. XRD (X-ray diffractron), SEM (scanning electron microscope) were used to analyze the crystal structure and microstructural sproperties of specimens. And also, $T_{O-T}$, TC were observed by the mesurement of temperature dependence of dielectric constant. Excellect physical properties of the piezoelectric constant $d_{33}$= 170 pC/N, electromechanical coupling factor kp= 0.312, Tc= $315^{\circ}C$ were obtained, respectively, from the specimen sintered at $1,080^{\circ}C$.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.205-205
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• 2008

PZT 세라믹은 우수한 유전 및 압전특성을 갖고 있어 변압기, 센서 및 엑츄에이터 등에 널리 응용되고 있다. 그러나, 우수한 특성에도 불구하고 PZT세라믹스의 소결시 PbO의 높은 유독성 및 휘발로 인하여 환경오염을 야기 시킨다. 그러므로 PbO로 구성된 세라믹을 대체하기 위한 우수한 압전특성을 가진 비납계 세라믹스 개발이 연구의 주류를 이루고 있다. 그 중 비납계 NKN와 BZT는 대체물질로 많이 관심을 받고 있다. 이는 일반적인 NKN조성은 우수한 압전성과 높은 큐리온도를 가지고 있을 뿐만 아니라, BZT조성의 Zr성분이 큐리온도를 낮추거나 유전특성을 졸게 하여 유전율 곡선을 완화하게 하는 특징이 있다. 하지만 NKN은 $1140^{\circ}C$이상의 소결온도에서 K의 휘발특성으로 인해 소성 후에도 주변의 수분을 흡수하는 조해성이 발생하는 문제가 발생한다. 그래서 본 연구에서는 낮은 온도에서 NKN계 세라믹스의 밀도를 증가시킬 뿐만 아니라, 우수한 유전 및 압전특성을 갖는 세라믹스를 제조하고자 비납계 $0.94(K_{0.5}Na_{0.5})NbO_3-0.06Ba(Zr_{0.05}Ti_{0.95})O_3$ (NKN-BZT)의 조성을 사용하였고 소결조제로는 $MnO_2$, NiO, $Bi_2O_3$, ZnO, $Li_2CO_3$, CuO등을 변화주어 유전 및 압전 특성을 알아보았다.

• 한국전기전자재료학회논문지
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• 제24권7호
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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.

• 한국전기전자재료학회논문지
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• 제24권7호
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• pp.559-562
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• 2011

In this study, the effect of $Nb_2O_5$ and sintering time on the positive temperature of coefficient of resistivity (PTCR) behavior of lead free $Ba_{0.99}(Bi_{0.5}Na_{0.5})_{0.01}TiO_3$ (BBNT) ceramics were investigated in order to fabricate a PTC thermistor with high $T_c$ temperature more than $140^{\circ}C$. In particular, BBNT ceramic doped with 0.1mol% $Nb_2O_5$ and sintered at $1350^{\circ}C$ for 4 h has significantly increased Curie temperature ($T_c$) of about $200^{\circ}C$, showed good PTCR behavior of room-temperature resistivity ($\rho_{rt}$) of $40{\Omega}{\cdot}cm$, a high $\rho_{max}/\rho_{min}$ ratio of $43.78{\times}10^3$ and a large resistivity temperature factor (${\alpha}$) of 16.1%/$^{\circ}C$. With increasing addition of $Nb_2O_5$ content, the $\rho_{rt}$ decreased to a minimum value of $40\;{\Omega}cm$ at 0.1mol% $Nb_2O_5$ and the $\rho_{rt}$ increased for x value over 0.1 mol%.

• 한국전기전자재료학회논문지
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• 제26권2호
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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.