• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.4
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• pp.205-209
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• 2016

In this paper, piezoelectric ceramics with the composition of $(Na_{0.525}K_{0.4425}Li_{0.0375})(Nb_{0.8975}Sb_{0.065}Ta_{0.0375})O_3+0.3wt%\;CoO+x\;CuO$ ($0.005{\leq}x{\leq}0.025$) (abbreviated to NKL-NST) were fabricated for ultrasonic sensor application. The effects of CuO addition and sintering on the microstructure and the piezoelectric properties of the NKL-NST ceramics were systematically studied. Excellent piezoelectric properties such as electromchanical coupling $factor(k_p)=0.415$, piezoelectric constant $(d_{33})=166pC/N$ and piezoelectric figure of merit $d_{{33}*}g_{33}=5.47pm^2/N$ were obtained from the 2.5 mol% CuO doped NKL-NST+0.3 wt%CoO ceramics sintered at $1,000^{\circ}C$ for 3 h.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.8
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• pp.707-711
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• 2006

ZnO was doped up to 0.3 wt% for improving the electrical properties of lead-free $[Li_{0.04}(Na_{0.44}Ko_{0.52})-(Nb_{0.86}\;Ta_{0.10}\;Sb_{0.04})]O_3$ piezoelectric ceramics. The ceramics were fabricated with the conventional sintering processes. Crystal structure of the samples was tetragonal phase regardless of ZnO amount. However, the piezoelectric properties were varied with the ZnO amount. The electro-mechanical coupling factor $(k_p)$ was with the ZnO amount up to 0.2 wt% but decreased with the further addition. the maximum value of $k_p$ was 0.475. Density, piezoelectric charge constant and relative dielectric constant was also showed maximum value at 0.2 wt%. The maximum values are $4.75g/cm^3$, 275 pC/N, 1403, respectively. In contrast, the mechanical quality factor $(Q_m)$ was not varied with increasing the ZnO addition up to 0.2 wt% but rapidly increased at 0.3 wt%.

• Journal of the Korean Ceramic Society
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• v.32 no.7
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• pp.839-845
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• 1995

The structural and dielectric properties of Pb(Mg1/3Nb2/3)O3 ceramics substituted by Nd3+, La3+, K+ and Na+ were studied over 0~50 at.% substituent content. The 1 : 1 ordering behavior of Mg2+ and Nb5+ ions in the B site sublattice was observed in Nd3+-and La3+-modified compounds. The degree of ordering was increased with Nd3+, La3+ content in the compounds. But K+-or Na+-modified compounds did not exhibit the ordering behavior. This was explained by charge and size effect of A and B site cations and oxygen vacancies. As the mole fractions of substituent increased, the maximum values of dielectric constants were rapidly decreased and the phase transitions were broadened. Phase transition temperature was correlated with the covalency of A-O and B-O bonding.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.4
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• pp.218-222
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• 2017

In this paper, in order to develop excellent composition ceramics for a piezoelectric energy- harvesting device, we synthesized $0.99(Na_{0.52}\;K_{0.443}\;Li_{0.037})(Nb_{0.883}\;Sb_{0.08}\;Ta_{0.037})O_3$ + $0.01(Sr_{0.95}Ca_{0.05})TiO_3$ + $0.3\;wt%\;Bi_2O_3\;+\;0.3\;wt%\;Fe_2O_3\;+\;0.3\;wt%\;CuO$ (abbreviated as NKN-SCT) ceramics with different sintering times, using the ordinary solid-state reaction method. The effect of sintering time on the microstructure and piezoelectric properties was investigated. The ceramics with the sintering time of 7 h have the optimum values of the piezoelectric constant ($d_{33}$), piezoelectric voltage constant ($g_{33}$), planar piezoelectric coupling coefficient (kp), mechanical quality factor (Qm), and dielectric constant (${\varepsilon}r$): $d_{33}=314[pC/N]$, $g_{33}=20.07[10^{-3}mV/N]$, kp = 0.442, Qm = 93, ${\varepsilon}r=1,768$, all being suitable for a piezoelectric energy-harvesting device.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.76-76
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• 2009

PZT세라믹스는 높은 압전특성과 우수한 큐리온도($400^{\circ}C$)를 보유하고 있어 오래시간에 걸쳐 주목받고 있다. 현재 압전변압기, 액츄에이터, 센서등의 압전소자는 PZT를 이용하여 제작하고 있지만 PZT는 고온 소결시 PbO의 휘발이 환경오염을 초래하며 인체의 유해하다는 연구결과가 나왔다. 이에 최근에는 PbO가 포함 되지않은 무연(lead-free)계 압전세라믹스가 주목받고 있다. 무연 압전 세라믹스의 종류로는 Bi-layer-structured ceramics, Bi-perovskite type ceramics, NKN base ceramics 가 존재하고 있다. 그 중 $(Na_{0.5}K_{0.5})NbO_3(NKN)$ 세라믹스는 높은 큐리온도와($400^{\circ}C$)와 높은 전기기계 결합계수(약 36%)를 보유하고 있어 많은 연구가 이루어 지고 있다. 하지만 NKN은 PZT에 비하여 치밀성이 낮으며 일반적인 산화물 소결방법으로는 밀도를 높이기가 어려운 단점이 존재한다. 이를 개선하기 위한 방법으로 hot pressing와 spak plasma sintering, RTGG와 같은 방법으로 밀도를 높일수 있지만 비용이 많이 들어 일반적으로 사용이 어렵다. 다른 방법으로 NKN에 첨가물을 넣는 방법을 사용하고 있는데 방법으로 $LiNbO_3$, $LiTiO_3$, $LiSbO_5$를 첨가하여 개선하는 방법이 있다. 본 실험은 첨가물을 넣는 방식으로 비화학양론적 $(Na_{0.5}K_{0.5})_{0.97}(Nb_{0.9}Ta_{0.1})O_3(NKNT)$조성에 CuO를 mol%로 변화주어 유전 및 압전 특성을 조사하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.188-189
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• 2009

In this study, in order to develop excellent lead-free composition ceramics for piezoelectric transformer, $(K_4CuNb_8O_{23})$ added $(K_{0.5}Na_{0.5})(Nb_{0.96}Sb_{0.04})O_3$ ceramics were fabricated using conventional mixed oxide method and their piezoelectric and dielectric properties were investigated as a function of the amount of KCN addition. With increasing the amount of KCN addition, density and mechanical quality factor(Qm), electromechanical coupling factor (Kp) were increased up to 1.2mol% and then decreased. At the 1.2mol% KCN added specimen, mechanical quality factor (Qm), electromechanical coupling factor (Kp), density and dielectric constant (${\varepsilon}r$) showed the optimal values of 781, 0.445, $4.42g/cm^3$ and 443, respectively, for piezoelectric transformer application.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.11
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• pp.690-693
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• 2015

In this paper, in order to develop excellent Pb-free composition ceramics for ultrasonic sensor. The $SnO_2$-doped ($Na_{0.525}K_{0.443}Li_{0.037})(Nb_{0.883}Sb_{0.08}Ta_{0.037})O_3$)(abbreviated as NKL-NST) ceramics have been synthesized using the ordinary solid state reaction method. The effect of $SnO_2$-doping on their dielectric and piezoelectric properties was investigated. The ceramics doped with 0 wt% $SnO_2$ have the optimum values of piezoelectric constant($d_{33}$), piezoelectric figure of merit($d_{33}.g_{33}$), planar piezoelectric coupling coefficient($k_p$) and density : $d_{33}=195[pC/N]$, $d_{33}.g_{33}=5.62pm^2/N.kp=0.40$, $density=4.436[g/cm^3]$. suitable for duplex ultrasonic sensor application.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.160-161
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• 2009

In this study, in order to develop the lead free piezoelectric ceramics with excellent piezoelectric properties, (Na,K)$NbO_3$ ceramics according to the amount CuO addition were fabricated using a conventional mixed oxide process and their piezoelectric and dielectric characteristics were investigated. At the 0.8mol% CuO added composition, density, electromechanical coupling factor(kp), echanical quality factor(Qm), dielectric constant$(\varepsilon_r$) and piezoelectric constant($d_{33}$) showed the optimum value of $4.459g/cm^3$, 0.469, 540, 410, 69.57pC/N, respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.10
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• pp.637-640
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• 2017

In this study, $(1-x)(Na_{0.52}K_{0.443}Li_{0.037})(Nb_{0.883}Sb_{0.08}Ta_{0.037})O_3-x(Bi_{0.5}(Na_{0.7}K_{0.3})_{0.5}ZrO_3$ ceramics were fabricated by BNKZ substitution using a conventional solid-state method to develop excellent lead-free piezoelectric ceramics for piezoelectric actuators; their dielectric and piezoelectric properties were then investigated. All specimens were in the orthorhombic phase. $NKL-NSTO_3$ ceramics with x=0.01 showed excellent piezoelectric properties. The density (${\rho}$), piezoelectric charge constant ($d_{33}$), planar piezoelectric coupling coefficient ($k_p$), mechanical quality factor ($Q_m$), and dielectric constant (${\varepsilon}_r$) had optimized values of $4.56g/cm^3$, 208 pC/N, 0.43, 96, and 975, respectively.

• 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 $1050^{\circ}C$.