• 폴리머
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• 제26권3호
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• pp.367-374
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• 2002

본 연구에서는 나노 입자의 카본블랙을 결정성 고분자에 분산시켜 특정한 온도에서 저항이 급격하게 증가하는 positive temperature coefficient resistance (PTCR) 특성을 연구하였다. 열가소성 수지를 이용한 PTCR 소재를 열처리에 의하여 고분자의 큐리온도를 조절할 수 있었다. 나노입자 카본블랙이 고분자 구조내에 고르게 분산이 되지 않고, 카본블랙의 함량이 과다하면 negative temperature coefficient resistance (NTCR) 현상이 발생하였다. 카본블랙의 함량과 내부전압을 조절함에 따라 발열 온도를 선정할 수 있었다. 카본블랙의 함량에 따라 전기 전도성이 다르게 나타났으며, 20 wt% 이상에서는 저항이 거의 일정하게 나타난다는 것을 확인하였다. 본 연구에서 제조된 PTCR 소재는 반복적인 가열 냉각에 따른 상온에서의 초기 저항의 변화가 거의 없어 재현성을 확인하였으며, 초기의 낮은 저항에 의한 순간적인 발열에 의하여 저온에서의 PTCR 성능이 향상되었다.

• 한국세라믹학회지
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• 제31권2호
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• pp.185-193
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• 1994

Effect of Sb2O3 addition on microstructure and the PTCR characteristic was investigated. The range of the Sb2O3 content and the sintering temperature showing semiconducting and PTCR characteristic, were 0.05~0.125 mol%, and over 130$0^{\circ}C$, respectively. We found that PTCR characteristic, that is, room-temperature resistivity and specific resistivity ration were dependent on the microstructure.

• 한국세라믹학회지
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• 제22권5호
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• pp.54-60
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• 1985

This study is concerned with the mechanism of PTCR in $BaTiO_3$ ceramics doped by $Nb^{+5}$ Since the vacancy compensation layer at the grain boundary of n-type doped $BaTiO_3$ ceramics has been known as a major factor for surface state to give PTCR phenomena the dependence of PTCR on such vacancy compensation layer was attemped to be confirmed experimentally in this study. For the experiment quenching and annealing at various temperature after sintering were adopted to induce difference in the thickness of vacancycompensation layer so as to exihibit difference of PTCReffect eachother. The TEX>$Ba^{++}$ cocentration at the grain and grain boundary was measured by EDAX to confirm the formation of the vacancy compensation layer. It was found that i)either decrease in the temperature for quenching ii) or increase in the temperature for annealing improves the PTCR effect clearly iii)increase in TEX>$Ba^{++}$ concentration at the grain boundary results in the improvement of PTCR effect. It was concluded that all the experimental results gave the evidence for the dependence of PTCR effect on the vacancy compensation layer at the grain boundary which had been induced possibly by the $Ba^{++}$ diffusion by the heat treatment conducted.

• 한국세라믹학회지
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• 제24권6호
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• pp.579-585
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• 1987

The effects of flux KCl and dopant Nb2O5 on the PTCR characteristics of BaTiO3 prepared by molten salt synthesis method have been investigated. As the amount of dopant Nb2O5 is over the solubility limit in BaTiO3, the room-temperature resistivity increases, and the PTCR effect and the grain size decrease. The variation of the amount of flux KCl slightly influences on the room-temperature resistivity, PTCR effect and grain size in Nb2O5 doped BaTiO3, but BaTiO3 ceramics prepared by the method of molten salt synthesis show larger PTCR effect than those of conventional calcining of mixed oxides.

• 한국세라믹학회지
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• 제24권2호
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• pp.111-116
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• 1987

By the method of direct wet process which has been developed in our laboratory, the high purity BaTiO3 powders could be synthesized from the room temperature to 90$^{\circ}C$ according to particle sizes. For to detect the PTCR effects, Sb2O3 wasdoped in the BaTiO3 powders which had been prepared on above method. As the results, the PTCR effects were in creased with the decreasing grain size of BaTiO3 powders.

• 한국세라믹학회지
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• 제39권1호
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• pp.16-20
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• 2002

Semiconducting (Ba.Sr)TiO$_3$ceramic device, which shows the PTCR effect, has been usually used as a current limiter. In this case, the device should endure the condition under the high electric field. In this study, the dynamic electrical properties of the PTCR device under high voltage has been evaluated. Two different formulated powders were used and the sintered bodies exhibited the different grain size and porosity. The wide range of characterization such as complex impedance spectroscopy, microstructure, I-V characteristics and voltage dependence of resistivity of the samples were performed. The PTCR effect of the specimen containing coarse grains was very sensitively dependent on the AC electric field, showing that it was inversely pro-portional to the grain boundary potential barrier. The withstanding voltage was proportional to the potential barrier of grain boundary.

• 한국재료학회지
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• 제14권2호
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• pp.115-120
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• 2004

Perovskite barium-strontium titanate, $(Ba, Sr)TiO_3$ was prepared and effects of $Sb_2$O$_3$ additives on its PTCR properties were investigated. $The (Ba,Sr)TiO_3$ with 0.05～0.25 mol% $Sb_2$$O_3$ showed semiconducting PTCR behavior and anomalous grain growth was also observed when it was sintered above $1330^{\circ}C$. It was considered that charge compensation by doping 8b203 as well as abnormal grain growth by sintering lead to resistivity reduction from insulating to semiconducting transition.

• 한국재료학회지
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• 제12권3호
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• pp.169-175
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• 2002

Semiconductive nano $(Ba_{1-x}Sb_x)TiO_3$ powders were synthesized by the hydrothermal process and Sb was simultaneously doped in the hydrothermal condition. $(Ba_{1-x}Sb_x)TiO_3$ powders obtained from optimum condition(at 20$0^{\circ}C$ for 3hr) exhibited spherical shape, high purity and nano size. The PTCR characteristics was observed when 0.1 and 0.2 mole% Sb were added and sintered at over 130$0^{\circ}C$ for 1 hour, respectively. And The ceramics exhibit the PTCR characteristics with a resistively jump $ratio($\rho$_{max}/$\rho$_{min})$ of about $10^4$. Also we found that PTCR characteristics were dependent on the microstructure.

• 한국세라믹학회지
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• 제34권7호
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• pp.703-712
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• 1997

The PTCR devices of BaTiO3 doped with Sb2O3, SiO2 were prepared by Liquid Addition Method(LPAM) where doping sources were used in the forms of Liquid. The amounts of doping in LPMA is smaller than that in solid state mixing method. Also the doping process in LPMA is very suitable for BaTiO3-based PTCR devices because it is easy to obtain homogeneous mixing and reproductivity. By optimizing the doping condition in BaTiO3 system, (0.09 mol% Sb2O3, 0.25 wt% SiO2 and 0.02 wt% MnO2) it was possible to fabricate BaTiO3-based PTCR devices whee the room-temperature resistivity and specific resistivity were 15{{{{ OMEGA }}cm and 2$\times$106 respectively.

• 한국분말재료학회지
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• 제18권1호
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• pp.41-48
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• 2011

As a pore precursor, carbon black with different content of 0 to 60 vol% were added to (Ba,Sr)$TiO_3$ powder. Porous (Ba,Sr)$TiO_3$ ceramics were prepared by pressureless sintering at $1350^{\circ}C$ for 1h under air. Effects of carbon black content on the microstructure and PTCR characteristics of porous (Ba,Sr)$TiO_3$ ceramics were investigated. The porosity of porous (Ba,Sr)$TiO_3$ ceramics increased from 6.97% to 18.22% and the grain size slightly decreased from $7.51\;{\mu}m$ to $5.96\;{\mu}m$ with increasing carbon black contents. PTCR jump of the (Ba,Sr)$TiO_3$ ceramics prepared by adding carbon black was more than $10^5$, and slightly increased with increasing carbon black. The PTCR jump in the (Ba,Sr)$TiO_3$ ceramics prepared by adding 40 vol% carbon black showed an excellent value of $9.68{\times}10^5$, which was above two times higher than that in (Ba,Sr)$TiO_3$ ceramics. These results correspond with Heywang model for the explanation of PTCR effect in (Ba,Sr)$TiO_3$ ceramics. It was considered that carbon black is an effective additive for preparing porous $BaTiO_3$ based ceramics. It is believed that newly prepared (Ba,Sr)$TiO_3$ cermics can be used for PTC thermistor.