• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.1324_1325
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• 2009

The heterolayered $BaTiO_3/(Bi_{0.5}Na_{0.5})TiO_3$ thick films were fabricated by screen printing techniques on alumina substrates electrodes with Pt. We report the improved ferroelectric properties in the heterolayered teteragonal/rhombohedral structure composed of the $BaTiO_3$ and the $(Bi_{0.5}Na_{0.5})TiO_3$ thick films. We investigated the effects of deposition conditions on the structural and electrical properties of the heterolayered BNT/BT thick films. The structural and electrical properties of the heterolayered BNT/BT thick films were studied. All PZT heterolayered thin films show dense and homogeneous structure without the presence of the rosette structure. The dielectric constant, loss and remanent polarization oft heheterolayered BNT/BT thick films were superior to those of single composition $BaTiO_3$ and $(Bi_{1/2}Na_{1/2})TiO_3$, and those values for the heterolayered BNT/BT thick films sintered at $1100^{\circ}C$ were 916, 0.79 and $12.63{\mu}C/cm^2$.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.32-32
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• 2008

Microstructure and positive temperature coefficient of resistivity (PTCR) characteristics of $0.9BaTiO_3-0.1(Bi_{0.5}Na_{0.5})TiO_3$ [BaBiNT] ceramics doped with $Nb_2O_5$ were investigated in order to develop the Pb-free high Curie temperature ($T_c$)(>$160^{\circ}C$) PTC thermistor. The BaBiNT ceramics showed a tetragonal perovskite structure, irrespective of the added amount of $Nb_2O_5$. They also have a homogeneous microstructure. The resistivity of BaBiNT ceramics was gradually decreased by doping $Nb_2O_5$, which might be due to $Nb^{+5}$ ions substituting for $Ti^{+4}$ sites. The PTCR characteristics of BaBiNT ceramics appeared when the amount of doped $Nb_2O_5$ exceeded 0.0025mol%. Moreover, the abrupt grain growth was observed for the 0.03mol% $Nb_2O_5$added BaBiNT ceramics. It showed an especially high $T_c$ of approximately $172^{\circ}C$ and good PTCR characteristics of a high $\rho_{max}/\rho_{min}$ ratio ($2.96\times10^3$), a high resistivity temperature factor (11.40/$^{\circ}C$) along with a relatively low resistivity ($3.5\times10^4\Omega{\cdot}cm$).

• 한국전기전자재료학회논문지
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• 제21권7호
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• pp.638-644
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• 2008

The effects of $Nb_2O_5$ and $MnO_2$ on the positive temperature coefficient of resistivity (PTCR) behavior of lead-free $Ba_{0.99}(Bi_{1/2}Na_{1/2})_{0.01}TiO_3$ (BaBiNT) ceramics were investigated in order to fabricate a PTC thermistor available at high temperature of > $120^{\circ}C$. In particular, 0.05 mol% $Nb_2O_5$ added BaBiNT ceramic, which has significantly increased Curie temperature (Tc) of $160^{\circ}C$, showed good PTCR behavior; low resistivity at room temperature $(\rho_r)$ of $80.1{\Omega}{\cdot}cm$, a high $\rho_{max}/\rho_{min}$ ratio of $5.65{\times}10^3$ and a large resistivity temperature factor (a) of 18.5%/$^{\circ}C$. Furthermore, the improved $\rho_{max}/\rho_{min}$ of $6.48{\times}10^4$ and a of 25.4%/$^{\circ}C$ along with higher $T_c$ of $167^{\circ}C$ despite slightly increased $\rho_r$ of $569{\Omega}{\cdot}cm$, could be obtained for the BaBiNT + 0.05 mol% $Nb_2O_5$ + 0.02 wt% $MnO_2$ ceramic cooled down at a rate of $200^{\circ}C/h$.

• 한국분말재료학회지
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• 제25권2호
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• pp.104-108
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• 2018

Grain-growth behavior in the $95Na_{1/2}Bi_{1/2}TiO_3-5BaTiO_3$ (mole fraction, NBT-5BT) system has been investigated with the addition of $Na_2CO_3$. When $Na_2CO_3$ is added to NBT-5BT, the growth rate is higher than desired and grains are already impinging each other during the initial stage of sintering. The grain size decreases as the sintering temperature increases. With the addition of $Na_2CO_3$, a liquid phase infiltrates the interfaces between grains during sintering. The interface structure can be changed to be more faceted and the interface migration rate can increase due to fast material transport through the liquid phase. As the sintering temperature increases, the impingement of abnormal grains increases because the number of abnormal grains increases. Therefore, the average grain size of abnormal grains can be decreased as the temperature increases. The phenomenon can provide evidence that grain coarsening in NBT-5BT with addition of $Na_2CO_3$ is governed by the growth of facet planes, which would occur via mixed control.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.251-251
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• 2007

A new type of a lead-free positive temperature coefficient of resistivity(PTCR) material. based on $(Bi_{1/2}Na_{1/2})TiO_3\;-\;BaTiO_3$ solid solution ceramics has been developed. The effect of $Nb_O_5$ and $Y_2O_3$ content on the electrical properties and the microstructure of (1-x) $(Bi_{1/2}Na_{1/2})TiO_3\;-\;x\;BaTiO_3$ (BNBT) ceramics made using a conventional mixed oxide process has been studied. The Curie Temperature was obviously increased with the increasing of $(B_{0.5}Na_{0.5})TiO_3$ content. The Y-doped BNBT ceramics(x=0.02) display low resistivity values of $10^2-10^3$ ohm*cm at room temperature and the Curie Temperature of $Tc=155^{\circ}C$.

• 한국분말재료학회지
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• 제13권2호
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• pp.119-123
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• 2006

The grain growth behavior of $0.95Na_{1/2}Bi_{1/2}TiO_{3}-0.05BaTiO_{3}$ (NBT-5BT) has been investigated with respect to the grain shape. The powder compacts of NBT-5BT were sintered at 1200 for various times. The corresponding equilibrium shape was a round-edged cube with flat {100}-faces. Abnormal grains were not observed in the specimens sintered for 1 to 12 h but abnormal grains appeared when sintered for 24 h. Before the formation of abnormal grains, a valley was observed in the measured grain size distribution of NBT-5BT, showing that the grain size distribution was a combination of two unimodal distributions. The present result suggests that the grain growth in NBT-5BT was governed by the growth of facet planes which would occur via 2-dimansional nucleation and growth.

• 한국전기전자재료학회논문지
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• 제24권9호
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• pp.723-727
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• 2011

0.935Ba$TiO_3$-0.065($Bi_{0.5}Na_{0.5}$)$TiO_3+xmol%MnO_2$ (BBNTM-x) ceramics with $0{\leq}x{\leq}0.05$ were fabricated with muffled sintering by a modified synthesis process. Their microstructure and enhanced positive temperature coefficient of resistivity (PTCR) characteristics were systematically investigated in order to obtain lead-free high TC PTCR thermistors. All specimens showed a perovskite structure with a tetragonal symmetry and no secondary phase was observed. Grain growth was achieved when the doped MnO2 was increased above 0.02 mol%. This is due to the effect of positive Mn ion doping as an acceptor compensating a Ba vacancy occurred by the higher donor dopant concentration of $Bi^{3+}$ ion. Especially, enhanced PTCR characteristics of the extremely low ${\rho}_{RT}$ of $9\;{\Omega}{\cdot}cm$, PTCR jump of $5.1{\times}10^3$, ${\alpha}$ of 15.5%/$^{\circ}C$ and high $T_C$ of $167^{\circ}C$ were achieved for the BBNTM-0.04 ceramics.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2009년도 추계학술발표대회
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• pp.31.1-31.1
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• 2009

In an approach to acclimate ourselves torecent ecological consciousness trend, a lead-free piezoelectric material, bismuth sodium titanate (abbreviated as BNT) based bismuth sodium barium titanate (abbreviated as BNT-BT), was considered as an environment-friendly alternative for a lead based piezoelectric system. Ceramic specimens of0.94[(BixNa0.5)TiO3]-0.06[BaTiO3] (x = 0.500~0.515) compositions were prepared by a modified mixed oxide method. To increase the chemical homogeneity andre action activity, high energy mechanical milling machine and pre-milled nanosized powder has been used. In this method (BixNa0.5)TiO3 (x=0.500~0.515) andBaTiO3 were prepared separately from pre-milled constituent materials at low calcination temperature and then separately prepared BNTX (X=1, 2, 3 and 4) and BT were mixed by high energy mechanical milling machine. Without further calcination step the mixed powders were pressed into disk shape and sintered at $1110^{\circ}C$. Microstructures, phase structures and electrical properties of the ceramic specimens were systematically investigated. Highly dense ceramic specimens with homogenous grains were prepared in spite of relatively low sintering temperature. Phase structures were not significantly influenced by the excess amount Bi. Large variation on the piezoelectric and dielectric properties was detected at relative high excess Bi amounts. When $x{\leq}0.505$, the specimens exhibit insignificant variation in piezoelectric and dielectric constant though depolarization temperature is found to be decreased. Considerable amount of decrease in piezoelectric and dielectric properties are observed with higher excess of Bi amounts ($x{\geq}0.505$). This research indicates the advantages of high energy mechanical milling and importance of proper maintenance of Bi stoichiometry.

• 한국재료학회지
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• 제17권2호
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• pp.68-72
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• 2007

Optimum compositions for piezoelectric properties of $(Bi_{0.5}Na_{0.5})_{(1-x)}Ba_xTiO_3$ ceramics were investigated in the range of $x=0{\sim}0.1$ covering rhombohedral to tetragonal phase regions. No impurity phases other than a perovskite phase were found and the grain size decreased with increasing x. A two-phase coexisting morphotropic phase area rather than boundary dividing rhombohedral and tetragonal phase regions appeared to exist at $x=0.05{\sim}0.08$. As for piezoelectric properties within morphotropic phase compositions, the piezoelectric constant ($d_{33}$) and the electromechanical coupling factor ($K_p$) showed peak values at x=0.065, 192 pC/N and 34%, respectively, indicating x=0.065 as an optimum composition for piezoelectric $(Bi_{0.5}Na_{0.5})_{(1-x)}Ba_xTiO_3$ ceramics.

• 한국전기전자재료학회논문지
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• 제24권7호
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• pp.559-562
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• 2011

In this study, the effect of $Nb_2O_5$ and sintering time on the positive temperature of coefficient of resistivity (PTCR) behavior of lead free $Ba_{0.99}(Bi_{0.5}Na_{0.5})_{0.01}TiO_3$ (BBNT) ceramics were investigated in order to fabricate a PTC thermistor with high $T_c$ temperature more than $140^{\circ}C$. In particular, BBNT ceramic doped with 0.1mol% $Nb_2O_5$ and sintered at $1350^{\circ}C$ for 4 h has significantly increased Curie temperature ($T_c$) of about $200^{\circ}C$, showed good PTCR behavior of room-temperature resistivity ($\rho_{rt}$) of $40{\Omega}{\cdot}cm$, a high $\rho_{max}/\rho_{min}$ ratio of $43.78{\times}10^3$ and a large resistivity temperature factor (${\alpha}$) of 16.1%/$^{\circ}C$. With increasing addition of $Nb_2O_5$ content, the $\rho_{rt}$ decreased to a minimum value of $40\;{\Omega}cm$ at 0.1mol% $Nb_2O_5$ and the $\rho_{rt}$ increased for x value over 0.1 mol%.