• Journal of the Korean Ceramic Society
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• v.43 no.11 s.294
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• pp.693-699
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• 2006

Textured $Bi_{0.5}(Na,K)_{0.5}TiO_3-BiFeO_3$ ceramics were prepared by the reactive-templated grain growth process, using platelike $Bi_4Ti_3O_{12}$ particles. The effects of chemical composition in $Bi_{0.5}(Na,K)_{0.5}TiO_3$ on texture development and densification were examined. Textured ceramics were obtained by using $Bi_{0.5}K_{0.5}TiO_3$ as an end member of the solid solution but densification was limited. Dense ceramics were obtained by using $Bi_{0.5}Na_{0.5}TiO_3$ but texture did not develop. Dense, textured ceramics were obtained by using $Bi_{0.5}(Na_{0.5}K_{0.5})_{0.5}TiO_3$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.1
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• pp.35-40
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• 2009

Lead free positive temperature coefficient of resistivity (PTCR) ceramics based on $BaTiO_3-(Bi_{0.5}Na_{0.5})TiO_3$ solid solution were prepared by a conventional solid state reaction method. The phase structure was showed single phase with perovskite structure regardless calcinations temperature and $Ba_{1-x}(Bi_{0.5}Na_{0.5})_xTiO_3$ structure was transformed from tetragonal to orthorhombic phase at $x{\geq}0.15$ mole. The XRD peaks with $45^{\circ}{\sim}46^{\circ}$ shifted in right the influence of crystal structure change and the intensity of peak was decreased with additive $(Bi_{0.5}Na_{0.5})TiO_3$. The curie temperature risen with additive $(Bi_{0.5}Na_{0.5})TiO_3$ but disappeared for $(Bi_{0.5}Na_{0.5})TiO_3$ addition more than 0.15 mole in TMA. In relative permittivity, the curie temperature by the transform of ferroelectric phase risen with additive $(Bi_{0.5}Na_{0.5})TiO_3$ but decreased in relative permittivity. Also, the peak of new curie temperature showed the sample containing $0.025{\sim}0.045$ mole of $(Bi_{0.5}Na_{0.5})TiO_3$ near $70^{\circ}C$ caused by phase transform from ferroelectric to ferroelectric and the peak of new curie temperature disappeared at 0.045 mole of $(Bi_{0.5}Na_{0.5})TiO_3$. In our study, it was found that the PTCR in $BaTiO_3-(Bi_{0.5}Na_{0.5})TiO_3$ system was possible for $0{\sim}0.025$ mole of $(Bi_{0.5}Na_{0.5})TiO_3$ and the maximum curie temperature by phase transition showed about at $145^{\circ}C$.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.11
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• pp.2093-2096
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• 2011

In this study, lead-free $(Na_{0.5}K_{0.5})NbO_3-BiTiO_3$ ceramics were fabricated by a conventional mixed oxide method. Structural and electrical properties of lead-free $(Na_{0.5}K_{0.5})NbO_3$ ceramics with the variation of $BiTiO_3$ were investigated. The results of X-ray diffraction analysis showed a typical polycrystalline perovskite structure without presence of the second phase in all specimens. Sintered density increased with an increasing of BTO and the specimen added with 0.07 mol% of $BiTiO_3$ showed the maximum value of 97.8%. Average grain size decreased and densification increased with an increasing of $BiTiO_3$ contents. The electromechanical coupling factor of the 0.01 mol% $BiTiO_3$ doped NKN specimens was 0.32. Dielectric constant, dielectric loss and Curie temperature of the 0.07 mol% $BiTiO_3$ doped NKN specimens were 1185, 0.145% and $400^{\circ}C$, respectively.

• Journal of the Korean Ceramic Society
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• v.32 no.8
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• pp.915-921
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• 1995

The morphotropic phase boundary and phase transitions of the solid solutiion system, (1-x)(Na1/2Bi1/2)TiO3-PbTiO3＋xPbTiO3 were studied by investigating changes in crystal structure, variations in permittivity with temperature, and calorimetric behavior. It was observed that the morphotropic phase boundary (MPB) of this solid solutiion system was at near 14 mol% of PbTiO3. Compositions containing less than 10mol% PbTiO3 (x<0.1) exhibited a phase transition, i.e. ferroelectric rhombohedrallongrightarrowparaelectric paraelectric cubic, with increasing temperature. Composition containing more than 14 mol% PbTiO3 (x 0.14) showed a phase transition from ferroelectric tetragonal to paraelectric cubic. In the composition range of 0.1$\varepsilon$ (T) curve, which coincided with a phase transition from ferroelectric rhombohedral to an intermediate phase, was also found.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.91-92
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• 2007

An anomalous positive temperature coefficient of electrical resistivity (PTCR) was investigated in a ferroelectric lead-free perovskite-type compound $(Bi_{0.5}Na_{0.5})TiO_3$ within $BaTiO_3$-based solid solution ceramics. The effect of $Nb_2O_5$ content on the electrical properties and the microstructure of (1 - x) $BaTiO_3-x\;(Bi_{0.5}Na_{0.5})TiO_3$ (BNT) ceramics made using a conventional mixed oxide process also has been studied. The Curie temperature was obviously increased with the increasing of $(Bi_{0.5}Na_{0.5})TIO_3$ content. The Nb - doped BNT ceramics (x=0.01) display low resistivity values of $10^{1{\circ}}C-10^{2{\circ}}C$ ohm.cm at room temperature and the Curie Temperature of $T_c=160^{\circ}C$.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1465-1466
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• 2011

We have studied structural and electrical properties of $(Na_{0.5}K_{0.5})NbO_3$ ceramics addition with $BiTiO_3$. The $(Na_{0.5}K_{0.5})NbO_3-BiTiO_3$ ceramics were fabricated by the conventional mixed oxide method, their dielectric and piezoelectric properties were investigated with the variations of additvie amount $BiTiO_3$. At the sintering temperature of $1130^{\circ}C$, the density, dielectric constant, grain size of 0.05mol% $BiTiO_3$ specimen showed the values of 4.69 g/$cm^3$, 898 and $24.8{\mu}m$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.57-58
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• 2008

PTC thermistor are characterized by an increase in the electrical resistance with temperature. The PTC materials of middle Curie point were produced or that of high Curie point (above $200^{\circ}C$), it was determined that compositional modifications of $Pb^{2+}$ for $Ba^{2+}$ produce change sin the Curie point to higher temperature. PTC ceramic materials with the Curie point above $120^{\circ}C$ were prepared by adding $PbTiO_3$, PbO or $Pb_3O_4$ into $BaTiO_3$. Thereby, adding $Pb^{2+}$ into $BaTiO_3$-based PTC material to improve Tc was studied broadly, however, weal know that PbO was poisonous and prone to volatilize, then to pollute the circumstance and hurt to people, so we should dope other innocuous additives instead of lead to increase Tc of composite PTC material. In order to prepare lead-free $BaTiO_3$-based PTC with middle Curie point, the incorporation on $Bi_{1/2}Na_{1/2}TiO_3$ into $BaTiO_3$-based ceramics was investigated on samples containing 0, 1, 2, 3, 4, and 50mol% of $Bi_{1/2}Na_{1/2}TiO_3$. $Bi_{1/2}Na_{1/2}TiO_3$ was compounded as standby material by conventional solid-state reaction technique. The starting materials were $Bi_{1/2}Na_{1/2}TiO_3$, $BaCO_3$, $TiO_2$ and $Y_2O_3$ powder, and using solid-state reaction method, too. The microstructures of samples were investigated by SEM, DSC, XRD and dielectric properties. Phase composition and lattice parameters were investigated by X-ray diffraction.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.7
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• pp.506-510
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• 2012

In this study, lead-free $(Na_{0.465}K_{0.465}Bi_{0.07})(Nb_{0.93}Ti_{0.07})O_3-0.08MnO_2$ ceramics were fabricated by conventional mixed oxide method. Structural and electrical properties of lead-free $(Na_{0.465}K_{0.465}Bi_{0.07})(Nb_{0.93}Ti_{0.07})O_3-0.08MnO_2$ ceramics with the variation of sintering temperature were investigated. As results of x-ray diffraction analysis, all specimens showed a typical polycrystalline perovskite structure without presence of the second phase. Sintered density increased with an increases of sintering temperature and the specimen sintered at $1,020^{\circ}C$ showed the maximum value of 4.5 $g/cm^3$. The average grain size of the $(Na_{0.465}K_{0.465}Bi_{0.07})(Nb_{0.93}Ti_{0.07})O_3-0.08MnO_2$ specimen sintered at $1,020^{\circ}C$ is about 0.83 ${\mu}m$. Electromechanical coupling factor, relative dielectric constant and dielectric loss of $(Na_{0.465}K_{0.465}Bi_{0.07})(Nb_{0.93}Ti_{0.07})O_3-0.08MnO_2$ specimens sintered at $1,020^{\circ}C$ were 0.252, 741 and 0.043% respectively.

• Journal of the Korean Ceramic Society
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• v.51 no.6
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• pp.527-532
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• 2014

$0.97Bi_{0.5+x}(Na_{0.78}K_{0.22})_{0.5-3x}TiO_3-0.03LaFeO_3$ lead-free piezoelectric ceramics were fabricated by a solid state reaction method. $LaFeO_3$ additives were added to $Bi_{0.5}(Na_{0.78}K_{0.22})_{0.5}TiO_3$ for volatile compensation of bismuth and sodium ions in the sintering process. To create A-site vacancies, the mole ratio and charge valence of A-site ions ($Bi^{3+}$, $Na^+$ and $K^+$) were controlled. The improved piezoelectric properties were observed by addition of $LaFeO_3$ and control of A-site vacancies. In particular, a $d_{33}^*(S_{max}/E_{max})$ value of 614pm/V and an electric field induced strain of 0.33% was observed in $0.97Bi_{0.505}(Na_{0.78}K_{0.22})_{0.485}TiO_3-0.03LaFeO_3$ ceramic.

• Korean Journal of Materials Research
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• v.20 no.11
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• pp.575-580
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• 2010

The microstructure and positive temperature coefficient of resistivity (PTCR) characteristics of 0.1 mol%$Na_2Ti_6O_{13}$ doped $0.94BaTiO_3-0.06(Bi_{0.5}Na_{0.5})TiO_3$ (BBNT-NT001) ceramics sintered at various temperatures from $1200^{\circ}C$ to $1350^{\circ}C$ were investigated in order to develop eco-friendly PTCR thermistors with a high Curie temperature ($T_C$). Resulting thermistors showed a perovskite structure with a tetragonal symmetry. When sintered at $1200^{\circ}C$, the specimen had a uniform microstructure with small grains. However, abnormally grown grains started to appear at $1250^{\circ}C$ and a homogeneous microstructure with large grains was exhibited when the sintering temperature reached $1325^{\circ}C$. When the temperature exceeded $1325^{\circ}C$, the grain growth was inhibited due to the numerous nucleation sites generated at the extremely high temperature. It is considered that $Na_2Ti_6O_{13}$ is responsible for the grain growth of the $0.94BaTiO_3-0.06(Bi_{0.5}Na_{0.5})TiO_3$) ceramics by forming a liquid phase during the sintering at around $1300^{\circ}C$. The grain growth of the BBNT-NT001 ceramics was significantly correlated with a decrease of resistivity. All the specimens were observed to have PTCR characteristics except for the sample sintered at $1200^{\circ}C$. The BBNT-NT001 ceramics had significantly decreased $\tilde{n}_{rt}$ and increased resistivity jump with increasing sintering temperature at from $1200^{\circ}C$ to $1325^{\circ}C$. Especially, the BBNT-NT001 ceramics sintered at $1325^{\circ}C$ exhibited superior PTCR characteristics of low resistivity at room temperature ($122\;{\Omega}{\cdot}cm$), high resistivity jump ($1.28{\times}10^4$), high resistivity temperature factor (20.4%/$^{\circ}C$), and a high Tc of $157.9^{\circ}C$.