• 한국전기전자재료학회논문지
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• 제24권9호
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• pp.728-732
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• 2011

In this study, piezoelectric and dielectric properties of Lead-free $0.97[(K_{0.5}Na_{0.5})(Nb_{0.97}Sb_{0.03})O_3]+0.03[(Bi_{0.5}K_{0.5})TiO_3]$ (abbreviated as 0.97NKNS-0.03BKT)ceramics synthesized by conventional solid-state reaction process were investigated as a function of $K_{5.4}Cu_{1.3}Ta_{10}O_{29}$ addition. The results indicated that the $K_{5.4}Cu_{1.3}Ta_{10}O_{29}$ addition significantly improved the sinterability, grain growth and piezoelctric properties of 0.97NKNS-0.03BKT ceramics. The optimum values as planar piezoelectric coupling coefficient ($k_p$= 0.355), piezoelectric constant ($d_{33}$= 207 pC/N) and mechanical quality factor ($Q_m$= 128) were obtained when 0.009KCT was added. The electromechanical coupling factor($k_p$) was slightly decreased according to the increasing temperature.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.2
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• pp.590-594
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• 2004

In this study, lead-free piezoelectric ceramics were investigated for pressure sensor applications as a function of the amount of $CeO_2$ addition at Bi(Na,K)$TiO_3-SrTiO_3$ system. With increasing the amount of $CeO_2$ addition, the density and dielectric constant increased. Electromechanical coupling factor($k_p$) showed the maximum value(kp, 0.39) at 0.1wt% $CeO_2$ addition and decreased above 0.1wt% $CeO_2$ addition., Density, dielectric constant(${\varepsilon}_r$) increased but mechanical quality factor(Qm), piezoelectric constant(d33) decreased in $CeO_2$ addition, respectively.

• 한국전기전자재료학회논문지
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• 제17권8호
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• pp.830-834
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• 2004

In this study, lead-free pirzoelectric ceramics were investigated for pressure sensor applications as a function of the amount of ${La}_2{O}_3$ addition at $Bi(Na, K)Ti{O}_3-SrTi{O}_3$system. With increasing the amount of addition, the density and dielectric constant increased up to 0.9 wt% ${La}_2{O}_3$ addition and decreased above 0.9 wt% ${La}_2{O}_3$addition. Electromechanical coupling factor( $K_{P}$) showed the maximum value at 0.2 wt% ${La}_2{O}_3$addition and decreased above 0.2 wt% ${La}_2{O}_3$ addition. Electromechanical coupling $factor{(K)}_P$, density, dielectric constant$(\varepsilon_\Gamma)$, piezoelectric constant$(d_33)$ and curie temperature$(T_C)$ showed optimum value of 0.40, 5.75 g/㎤, 768, 215 pC/N and 320 $^{\circ}C$ at 0.2 wt%${La}_2{O}_3$addition, respectively.

• 한국세라믹학회지
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• 제45권5호
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• pp.263-267
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• 2008

$(Bi_{1/2}Na_{1/2})TiO_3$-based ceramics have been intensively studied as lead-free piezoelectric ceramics. In this study, the piezoelectric properties and phase transition behaviors of BNT based solid solution $(Bi_{0.5}Na_{0.5})_{1-x}Ca_xTiO_3$ ($X=0.01{\sim}0.25$) were investigated. The morphotropic phase boundary(MPB) zone which BNT is transformed from rhombohedral to cubic structure was appeared by adding $CaTiO_3$ with 0.12 mol by the measurement of permittivity and X-ray diffraction. The behavior which ferroelectric BNT with adding $CaTiO_3$ was changed to antiferroelectric and paraelectric state was confirmed by the measurement ofhysterisis loop and depolarization temperature as a function of temperature. As $CaTiO_3$ concentration was increased, the phase transition temperature was decreased. The piezoelectric properties were highest at 0.01 mol of $CaTiO_3$ concentration. The electromechanical coupling factor($K_t$) and mechanical quality factor($Q_m$) were 42% and 254, respectively.

• Transactions on Electrical and Electronic Materials
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• 제16권4호
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• pp.179-182
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• 2015

The particle sizes of 0.95(K_0.5Na_0.5)NbO₃-0.05BaTiO₃ powder were controlled by secondary milling time after calcination. The average particle sizes, Dmean, of 0.95(K_0.5Na_0.5)NbO₃-0.05BaTiO₃ powders were critically changed from 14.31 μm to 0.91 μm by secondary milling time. The dielectric and piezoelectric properties of 0.95(K_0.5Na_0.5)NbO₃-0.05BaTiO₃ ceramics depended on the particle sizes of powders after calcination and the secondary milling process. As secondary milling times after calcination were increased to more than 48 hr, the dielectric and piezoelectric properties of 0.95(K_0.5Na_0.5)NbO₃-0.05BaTiO₃ ceramics were deteriorated.

• 한국분말재료학회지
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• 제17권5호
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• pp.399-403
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• 2010

The effects of $MnO_2$ doping on the crystal structure, ferroelectric, and piezoelectric properties of (K,Na)$NbO_3$ (KNN) ceramics have been investigated. $MnO_2$ was found to be effective in enhancing the densification and grain growth during sintering. X-ray diffraction analysis indicated that Mn ions substituted B-site Nb ions up to 2 mol%, however, further doping induced unwanted secondary phases. In comparison with undoped KNN ceramics, the well developed microstructure and the substitution to B-sites in 2 mol% Mn-doped KNN ceramics resulted in significant improvements in both piezoelectric coupling coefficient and electromechanical quality factor.

• 한국전기전자재료학회논문지
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• 제27권6호
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• pp.361-366
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• 2014

$MnO_2$-doped $0.985[Li_{0.04}(Na_{0.545}K_{0.46})_{0.96}(Nb_{0.81}Ta_{0.15}Sb_{0.04})]O_3+0.015KNbO_3(0.985LNKNTS+0.015KNbO_3)$ lead-free ceramics were fabricated by conventional solid state method to develop excellent dielectric and piezoelectric properties. The result of X-ray diffraction patterns obviously indicated that all of the specimen has pure perovskite structure without secondary phase. In addition, orthorhombic phase and coexistance region of orthorhombic-tetragonal phase (MPB) were observed with amount of $MnO_2$. The optimal values of ${\rho}$=4.70 $g/cm^3$, $d_{33}=238$ pC/N, $k_P=0.46$, $Q_m=121$, ${\varepsilon}_r=849$, and $T_C=225^{\circ}C$ were obtained at 0.01 mol% $MnO_2$ doped $0.985LNKNTS+0.015KNbO_3$ ceramics sintered at $990^{\circ}C$ for 5 h, respectively. Hence, it was indicated that the suitable amount of $MnO_2$ could improve the electrical properties of $0.985[Li_{0.04}(Na_{0.545}K_{0.46})_{0.96}(Nb_{0.81}Ta_{0.15}Sb_{0.04})]O_3+0.015KNbO_3$ ceramics.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.2
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• pp.660-663
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• 2003

In this Study, lead-free $Bi_{0.5}(Na_{0.84}K_{0.16})_{0.5}TiO_3$ system ceramics were fabricated with the variations of Sr substitution and their dielectric and piezoelectric characteristics were investigated. With the increase of Sr substitution, dielectric constant increased linearly and Curie temperature decreased slightly. Also, the temperature dependence curve of dielectric constant was moved to left-ward. At 4mol% Sr substitution, Tc of 292, kp of 34.03%, kt of 45.32% and ${\epsilon}r$ of 868 were shown, respectively.

• Transactions on Electrical and Electronic Materials
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• 제18권1호
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• pp.1-6
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• 2017

A comparative study of microwave and conventional sintering of lead-free $Bi_{1/2}(Na_{0.82}K_{0.18})_{1/2}TiO_3-BaZrO_3-CuO$ ceramics is presented. It was found that microwave sintering (MWS) can be successfully applied to the fabrication of large strain Bi-perovskite with electric field-induced strains comparable to those obtained with conventional sintering (CFS). Although MWS resulted in smaller grained microstructures than CFS, the ferroelectric properties were stronger in MWS-derived specimens than in the CFS-derived ones. The piezoelectric strain constant $d_{33}{^*}$ of the CFS-derived specimens reached a maximum value of 372 pm/V after sintering at $1100^{\circ}C$, whereas that of MWS-derived specimens peaked at $950^{\circ}C$ with a $d_{33}{^*}$ value of 324 pm/V.

• 한국전기전자재료학회논문지
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• 제34권1호
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• pp.1-7
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• 2021

This study investigated the structural, dielectric, ferroelectric, and strain properties of (0.98-x)Bi1/2Na1/2TiO3-0.02BiFeO3-xSrTiO3 (BNT-BF-100xST, x＝0.20, 0.22, 0.24, 0.26, and 0.28). All samples were successfully synthesized using the conventional solid-state reaction method and sintered at 1,175℃ for 2 h. The average grain size of the BNT-BF-100x ceramics decreased with increasing ST content. Furthermore, we observed that the ferroelectric- relaxor transition temperature (TF-R) decreased with increasing ST content, which eventually vanished in the BNT-BF-24ST ceramics. The results indicated that a ferroelectric to relaxor phase transition could be induced by ST modification. Consequently, a large electromechanical strain of 633 pm/V at 4 kV/mm was observed for the BNT-BF-26ST ceramics. These results imply that our materials have the competitive advantage of larger strain under lower operating field conditions compared with other BNT-based lead-free piezoelectric ceramics. We expect that BNT-BF-ST lead-free piezoelectric ceramics are promising candidates as a novel ternary BNT-based system and can find potential applications in actuators.