• 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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• 제25권7호
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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.

• 한국세라믹학회지
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• 제35권9호
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• pp.895-898
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• 1998

• 한국전기전자재료학회논문지
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• 제27권11호
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• pp.702-706
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• 2014

A comparative study has been attempted for microwave and conventional sintering of lead-free $Bi_{0.5}Na_{0.5}TiO_3(BNT)$-based multilayer ceramic actuators(MLAs). It was found that microwave sintering (MWS) could be successfully applied to the co-firing of piezoceramic/AgPd MLAs with a 10 times shorter firing cycle as well as $100^{\circ}C$ lower firing temperature ($850^{\circ}C$) for sufficient densification than conventional furnace sintering ($950^{\circ}C$). Furthermore, MWS-derived specimens showed better electric field-induced strain than that of CFS-derived specimens by effectively suppressing interdiffusions between ceramic and electrode layers.

• 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.

• 한국전기전자재료학회논문지
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• 제30권5호
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• pp.284-287
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• 2017

The electrocaloric effect in $0.94(Bi_{0.5}Na_{0.5})TiO_3+0.06KNbO3+0.9wt%$ G.F.ferroelectricceramics was observed in terms of the temperature change (${\Delta}T$) of the fabricated ceramics, Curie temperature $T_c$, and applied electric field. The specimens were fabricated by a conventional solid-state reaction. $T_c$ appeared near $165{\sim}170^{\circ}C$. The P-E hysteresis showed a tendency to slim down with a temperature increase and finally was slimmest near $150^{\circ}C$. With the increase of temperature, the polarization revealed a gradual decrease, and a sharp decline near $T_c$. When an electric field of 45 kV/cm was applied, the largest polarization was shown. The maximum value of the temperature change (${\Delta}T=0.31^{\circ}C$) was obtained at $165^{\circ}C$ under an applied electric field of 45 kV/cm.

• 한국전기전자재료학회논문지
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• 제29권12호
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• pp.764-768
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• 2016

To investigate excess $Na^+$ effect, $Bi_{0.5}(Na_{0.78+x}K_{0.22})_{0.5}TiO_3$ ($0{\leq}x{\leq}0.05$) (BNKT) ceramics were prepared by using a conventional solid-state reaction method. The structure and ferroelectric properties of BNKT ceramics were characterized by XRD (X-ray diffraction) and polarization dependence by external electric field. Also, the temperature dependence of dielectric constant and loss were studied. From these results, it was found that appropriate excess $Na^+$ into BNKT ceramics compensate the volatility and induce dense ceramics. The enhanced piezoelectric coefficient (158 pC/N) and depolarization temperature ($202^{\circ}C$) were obtained for the x=0.01 composition.

• Bulletin of the Korean Chemical Society
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• 제33권7호
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• pp.2305-2308
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• 2012

Perovskite structured barium titanate particles ($BaTiO_3$) platelets were synthesized by molten salt synthesis and topochemical microcrystal conversion. As the precursors of $BaTiO_3$, plate-like $BaBi_4Ti_4O_{15}$ particles were first synthesized by the reaction of $Bi_4Ti_3O_{12}$, $BaCO_3$, and $TiO_2$ at $1080^{\circ}C$ for 3 h in $BaCl_2$-KCl molten salt. After the topochemical reactions, layer-structured $BaBi_4Ti_4O_{15}$ particles transformed to the perovskite $BaTiO_3$ platelets. $BaTiO_3$ particles with thickness of approximately $0.5{\mu}m$ and a length of $10-15{\mu}m$ retained the morphology feature of the $BaBi_4Ti_4O_{15}$ precursor. For <001> $Pb(Mg_{1/3}Nb_{2/3})O_3-32.5PbTiO_3$ (PMNT)-5 wt % PbO piezoelectric ceramics textured with 5 vol % of $BaTiO_3$ templates, the Lotgering factor reached 0.82, and $d_{33}$ was 870 pC/N.

• 한국결정성장학회지
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• 제13권6호
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• pp.272-278
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• 2003

초음파 분무에 의한 유기금속 화학증착법 (MOCVD)법으로 $Bi_4Ti_3O_{12}$(BIT)와 Bi와 Ti 대신에 La과 V을 동시에 치환시킨 ($Bi_{3.75}La_{0.75})(Ti_{2.97}V_{0.03})O_{12}$ (BLTV)박막을 ITO/glass 기판 위에 증착하였다. 산소 분위기에서 30분 동안 증착한 후, RTA 방식의 직접삽입법으로 열처리를 하였다. 박막은 페로브스카이트상 생성 온도, 미세구조, 전기적 성질에 관해서 조사하였다. XRD(X-Ray diffraction) 측정결과 BLTV 박막의 페로브스카이트상 생성 온도는 약 $600^{\circ}C$로써 BIT의 $650^{\circ}C$보다 더 낮았다. BLTV 박막의 누설전류는 인가전압 1 V에서 $1.52\times10^{-19}$ A/cm^2$로 측정되었다 또한, $650^{\circ}C$에서 증착했을 경우 잔류 분극값이 $5.6\mu$C/$cm^2$, 항전계값 96.5 kV/cm으로 명확한 강유전성을 보이고 있다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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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.