• Korean Journal of Materials Research
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• v.29 no.4
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• pp.205-210
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• 2019

$Pb(Zr,Ti)O_3$ (PZT) is used for the various piezoelectric devices owing to its high piezoelectric properties. However, lead (Pb), which is contained in PZT, causes various environment contaminations. $(K,Na)NbO_3$ (NKN) is the most well-known candidate for a lead-free composition to replace PZT. A single crystal has excellent piezoelectric-properties and its properties can be changed by changing the orientation direction. It is hard to fabricate a NKN single crystal due to the sodium and potassium. Thus, $(Na,K)NbO_3-Ba(Cu,Nb)O_3$ (NKN-BCuN) is chosen to fabricate the single crystal with relative ease. NKN-BCuN pellets consist of two parts, yellow single crystals and gray poly-crystals that contain copper. The area that has a large amount of copper particles may melt at low temperature but not the other areas. The liquid phase may be responsible for the abnormal grain growth in NKN-BCuN ceramics. The dielectric constant and tan ${\delta}$ are measured to be 684 and 0.036 at 1 kHz in NKN-BCuN, respectively. The coercive field and remnant polarization are 14 kV/cm and $20{\mu}C/cm^2$.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.4
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• pp.801-804
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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.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.50.1-50.1
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• 2011

Lead-free ceramics with a composition of 0.55 mol%$K_4CuNb_8O_23-(K_{1-x}Na_x)NbO_3$ (KCN-KNNx) where $0.45{\leq}x{\leq}0.60$ were synthesized by conventional ceramic processing. Results revealed that the addition of Na was effective in changing the microstructure and relative density of KCN-KNNx. Further, the addition of Na resulted in a slight shift of the phase transition temperatures (To-t and Tc) toward low values. A high mechanical quality factor (Qm) of 1850 was found atx=0.54, which might be due to the build-up of an internal bias field (Ei) within KCN. Thermal hysteresis in KNNx was confirmed with an increase in the Na content during the heating and cooling cycles, resulting from structural changes. Thus, KCN-KNNx with x=0.54 exhibits excellent piezoelectric properties with d33 (97 pC/N), kp (36%), and Qm (1850), being promising candidates for application in high-power piezoelectric devices.

• Journal of Ceramic Processing Research
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• v.13 no.spc2
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• pp.174-176
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• 2012

Piezoelectric 0.93(Na0.5K0.5)NbO3-0.07BiTiO3 (NKN-BTO) ceramics were fabricated by the mixed-oxide method and their structural and dielectric properties was investigated with the variation of sintering temperature. All specimens were crystallized in the perovskite single phase without any formation of a second phase such as pyrochlore. The average grain size of the NKN-BTO specimen sintered at 1130 ℃ is 0.32 ㎛. The specimen sintered at 1100 ℃ showed the highest relative density of 98%. Electromechanical coupling factor, relative dielectric constant and dielectric loss of the NKN-BTO specimens sintered at 1110 ℃ were 0.31, 1222 and 0.02, respectively. Curie temperature of the specimen sintered at 1110 ℃ was 445 ℃.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.93-93
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• 2009

In this study, in order to develop excellent lead-free composition ceramics for piezoelectric transformer, $(K_{5.4}Cu_{1.3}Ta_{10}O_{29})$ added $(K_{0.5}Na_{0.5}](Nb_{0.97}Sb_{0.03})O_3$ were fabricated using conventional mixed oxide method. At the 0.9mol% KCT added specimen, electromechanical coupling factor(kp) and mechanical quality factor ($Q_m$) showed the optimal values of 0.437 and 727.07, respectively, for piezoelectric transformer application.

• 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.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1400-1401
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• 2006

In this study, in order to develop low temperature sintering piezoelectric ceramics for multilayer piezoelectric actuator, $PbSr(Mn_{1/3}Nb_{2/3})O_3-(Mg_{1/3}Nb_{2/3})O_3-(ZrTi)O_3$ ceramics were fabricated using $Na_{2}CO_{3}-Li_{2}CO_{3}$ as sintering aids and their piezoelectric and dielectric characteristics were investigated according to the sintering tempo rature. At the sintering temperature of $900^{\circ}C$, the density, electrom echanical coupling factor(kp), mechanical quality factor(Qm) and dielectric constant(${\varepsilon}r$) of specimen showed the optimum value of $7.730[g/cm^2]$, 0.552, 1134, 1492 and 330[pC/N], respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.48-48
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• 2008

현재 압전재료로써 사용되고 있는 PZT계 세라믹스는 우수한 압전 및 유전특성으로 초음파 센서, 압전변압기, 액츄에이터, 필터, 레조네이터와 같은 여러 응용분야에 널리 사용되어지고 있다. 그러나 납을 60%이상 포함하므로 환경오염에 의하여 그 사용에 대한 규제가 강화되고 있어 최근에는 납을 함유하지 않은 무연 환경친화형 압전세라믹스가 주목받고 있다. 현재 무연 조성 세라믹스에는 텅스텐-브론즈 형, 비스머스 레이어형, 페로브스카이트 형 등이 이으며, 그 중 페로보스카이트 혈을 제외하고는 보통 소성법 조제시 낮은 압전특성을 갖는다. 그러므로 압전특성을 증가시키기 위하여 Hot pressing, Hot forging, RTGG(Reactive Template Grain Growth), SPS(Spark Plasma Sintering), 그러나 이는 무연 세라믹스의 대량생산 과정에서 어려운 문제를 가지고 있고, 저가격 관점에서 볼 때 보통소성법이 보다 바람직하다. 그래서 보통소성법으로 NKN세라믹스의 소결성을 향상 시키고 비교적 높은 압전특성을 얻기 위해서 $LiSbO_3$, $LiNbO_3$, $LiTaO_3$, alkaline-earth(Mg, Ca, Sr, Ba) 등을 첨가한 논문들이 보고되고 있으며, 이러한 재료들의 kp는 대략 0.3-0.4를 나타내고 있다. 따라서, 본 연구에서는 소결온도를 낮추고자 $Ag_2O$를 소결조제로 사용하였고 유전 및 압전특성을 높이고자 소결시간 변화시켜 시편을 제작하여 NKN 세라믹스의 유전 및 압전특성을 조사하였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.8
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• pp.627-631
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• 2011

[ $[Li_{0.04}(Na_{0.54}K_{0.46})_{0.96}](Nb_{1-0.04-X}TaxSb_{0.04})O_3$ ]lead-free piezoelectric ceramics have been prepared by normal sintering at $1,100^{\circ}C$ for 5 h. X-ray diffraction analysis indicated that specimens demonstrate orthorhombic symmetry when $Ta\leq5$ mol%. While transforming into tetragonal symmetry when $x\geq20$ mol%. These suggest that the orthorhombic and tetragonal phases co-exist in the ceramics with 5 mol% $cm^3$. As the result of SEM images, the grain growth was decreased with the increase of Ta substitution. The ceramics become 'softening', leading to improvements in $k_p$, $\varepsilon_r$ and $d_{33}$, but a decrease in $Q_m$. Excellent properties of $k_p$= 0.46, $d_{33}$= 293 pC/N, ${\varepsilon}_r$= 1,583 and Tc= $340^{\circ}C$ were obtained when Ta= 15 mol%.

• Journal of the Korean Ceramic Society
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• v.53 no.2
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• pp.145-149
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• 2016

$(Bi_{1/2}Na_{1/2})_{0.94}Ba_{0.06}(Ti_{1-x}Nb_x)O_3$ (BNBTxNb) ceramics were investigated in terms of the crystal structure as well as the ferroelectric, dielectric, and piezoelectric properties. While little change was observed in the microstructure except for a slight decrease in the average grain size, a significant change was noticed in the temperature dependence of dielectric and piezoelectric properties. It was shown that the property changes are closely related to the downward shift in the position of the ferroelectric-to-relaxor transition temperature with increasing amount of Nb doping. A special emphasis is put on the fact that Nb doping is so effective at decreasing the ferroelectric-to-relaxor transition temperature that even at no more than 2 at.% Nb addition, the transition temperature was already brought down slightly below room temperature, resulting in the birth of a large strain at 0.46 %, equivalent to $S_{max}/E_{max}=767pm/V$.