• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.29.2-29.2
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• 2011

B-site substitution with isovalent and donor impurities was compared in terms of the piezoelectric properties of Bi-based ABO3 perovskite ceramics. X-ray diffraction study revealed that both impurities bring about degradation in their ferroelectric properties as well as piezoelectric characteristics. However, there existed a difference between the isovalent and heterovalent impurities that influence a phase transformation of ferroelectric anisotropic-to-electrostrictive pseudocubic symmetry. Based upon analyses including the crystal, microstructure, dielectric, ferroelectric properties, we believed that A-site vacancies in the ABO3 ceramic significantly contribute to a ferroelectric-nonpolar phase transition, which give rise to lead to a giant strains. The present paper will discuss the origin of giant strains in Bi-based perovskite ceramics.

• Journal of the Korean Ceramic Society
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• v.52 no.4
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• pp.237-242
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• 2015

$Bi_{0.5}(Na_{0.78}K_{0.22})_{0.5}TiO_3$ (BNKT) lead-free piezoelectric ceramics modified by $LaMnO_3$ (LM) were fabricated by conventional solid-state method. The crystal structure and the morphology of the lead free ceramics were analyzed by XRD (X-ray diffraction) and FE-SEM (Field Emission Scanning Electron Microscopy). The LM modified BNKT ceramics have a phase transition from ferroelectric tetragonal to non-polar pseudo-cubic. Despite decreases in the remnant polarization ($P_r$) and coercive field ($E_c$) in the P-E hysteresis loops, the electric-field induced strain properties were significantly enhanced by the LM modification. The highest value of $S_{max}/E_{max}=412pm/V$ at an applied electric field of 5 kV/mm was found in BNKT-0.01LM ceramic.

• 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.

• 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.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.1
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• pp.35-39
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• 2019

In this study, we investigated the optimum calcination temperature of lead-free $0.74(Bi_{0.5}Na_{0.5})TiO_3-0.26SrTiO_3$(BNST) piezoelectric ceramics by analyzing the crystal structure, dielectric properties, and electric field-induced strain behavior. BNST ceramics prepared by conventional solid-state reaction methods at various calcination temperatures according to the industrial standard. All samples of BNST ceramics were subsequently sintered at $1,175^{\circ}C$ for 2 h. Crystal structure classification of the ceramics showed a single perovskite phase, with no second phase detectable for the samples calcined at $750^{\circ}C$ or higher. BNST samples calcined at $850^{\circ}C$ exhibited the most optimal values for itsand the common physical parameters of $density=5.518g/cm^3$, ${\varepsilon}=1,871.837$, $tan{\delta}=0.047$, and ${d_{33}}^*=874pm/V$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.11
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• pp.925-929
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• 2009

In this study, $0.95(K_{0.5}Na_{0.5})NbO_3-0.05Li(Sb_{0.8}Nb_{0.2})O_3$ ceramics were investigated as a function of the amount of $Ag_2O$ addition in order to improve dielectric and piezoelectric properties of lead-free piezoelectric ceramics. With increasing the amount of $Ag_2O$ addition, density and electromechanical coupling factor ($k_p$) increased up to 0.2 wt.% $Ag_2O$ and decreased above 0.2 wt.% $Ag_2O$. At the sintering temperature of $1020^{\circ}C$, electromechanical coupling factor ($k_p$), density, dielectric constant (${\varepsilon}r$) and curie temperature (Tc) of ceramics with 0.2 wt% $Ag_2O$ showed the optimal values of 0.42, $4.33\;g/cm^3$, 738 and $393^{\circ}C$, respectively.

• Journal of the Korean Ceramic Society
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• v.56 no.6
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• pp.549-557
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• 2019

More than two decades of world-wide research efforts have resulted in several classes of potentially important materials. Among them are incipient piezoelectrics, which are especially useful for actuator applications. However, relatively large electric fields are required for activating the large incipient electromechanical strains. So far, many attempts have been made to reduce the required electric field by intentionally inhomogenizing the electric field distribution in the microstructure through core-shell and composite approaches. Here, we show that electric field concentration can be realized simply by adjusting electrode patterns. We have investigated the effect of electrode patterning on the incipient electromechanical strain properties of an exemplarily chosen lead-free relaxor system, revealing that electrode patterning does have a significant role on the strain properties of the given lead-free relaxor system. We believe that this approach would make a new strategy for ones to consider bringing the functional properties of electroceramics beyond their conventional limit.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.5
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• pp.292-296
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• 2014

We investigated the effect of Ta doping on the dielectric and piezoelectric properties of lead-free $(K_{0.5}Na_{0.5})NbO_3$ ceramics prepared using a conventional ceramic processing. X-ray diffraction analysis revealed that Ta was perfectly substituted into Nb-sites in the range of 0 to 20 at%. As Ta content in the KNN increased, the sinterability of KNN ceramics was significantly degraded while the Ta doping enhanced the piezoelectric constant $d_{33}$, planar mode piezoelectric coupling coefficient ($k_p$), and electromechanical quality factor ($Q_m$). The highest values for $d_{33}$, $k_p$, and $Q_m$ was found to be 156 pC/N, 0.37, and 155, respectively.

• Ceramist
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• v.23 no.1
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• pp.89-100
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• 2020

Abnormally large electromechanical strain properties have been reported in bismuth-based piezoelectric ceramics, which cast a promise for replacing the market-dominating PZT-based piezoelectric ceramics in actuator applications. In spite of these large strains in bismuth-based piezoelectric ceramics, there still remains a critical issue for its safe transfer to practical applications, representatively, a relatively high operating field required to obtain the large strain properties. To overcome the challenge, much attention has been paid to so-called 0-3(or 3-0) type ceramic/ceramic composite approach to better tailoring the strain properties of bismuth-based piezoelectric ceramics. The approach turns out to be highly effective, leading to a drastic decrease in the operating electric field for these materials. Besides, both extensive and intensive search for the related mechanism revealed that the reduction in the operating electric field is largely due to the contribution from polarization coupling or strain coupling model between two different ceramics. This article reviews the status of the art in the development of novel ceramic/ceramic composites to make large incipient piezostrains in bismuth-based lead-free piezoelectric ceramics practical.

• Journal of the Korean Ceramic Society
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• v.45 no.5
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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.