• Polymer(Korea)
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• v.26 no.3
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• pp.367-374
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• 2002

Electrical characteristics of crystalline polymer composites filled with nano-sized carbon black particle were studied. The developed composite system exhibited a typical positive temperature coefficient resistance (PTCR) characteristic, where the electrical resistance sharply increased at a specific temperature. The PTCR effect was sometimes followed by a negative temperature coefficient resistance (NTCR) feature with temperature, which seemingly caused by the coagulation of nano-sized carbon black particles in the excessive quantity. The PTCR temperature was controlled by the carbon black content and the external voltage. The change of electric conductivity was shown as a function of carbon black content, and the resistance was constant when the carbon black content was over 20 wt%. The room-temperature resistance was maintained by a repeated heating and cooling. The excellent PTCR characteristic was demonstrated by the low resistance in the initial stage and the instantaneous heating capability.

• Journal of the Korean Ceramic Society
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• v.40 no.10
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• pp.921-924
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• 2003

A current-voltage relation for Positive Temperature Coefficient of Resistance (PTCR) ceramic was derived and compared with the experimental data. The new current-voltage relation was developed based on Heywangs double Schottky barrier model and a bias distribution across the grain boundary. The voltage limitation V < 4${\Phi}$$\sub$b/ suggested by Heywang is no longer necessary in the new expression for the voltage dependence of the resistance. The pulsed voltages were applied to the PTCR ceramic specimen in order to avoid possible temperature variation during the measurement.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.7
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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%.

• Journal of the Korean Ceramic Society
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• v.22 no.3
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• pp.46-52
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• 1985

(Ba0.8. Sr0.2) $TiO_3$ semiconducting ceramic with and without Ti-excess composition were prepared by various sintering temperature. The effects of Ti compositions on the samples were discussed in terms of color micro-structure resistivity at room temperature and the positive temperature coefficient resistivity(PTCR). The 1.02mol Ti-excess composition provides better PTCR properties and has uniform micrositructures with 5-7${\mu}{\textrm}{m}$.

• 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 $157.9^{\circ}C$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.3
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• pp.217-221
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• 2008

In this study, We have been investigated the effect of calcination temperature and high-energy ball-milling of powder influences the $BaTiO_3$-based PTCR(Positive Temperature coefficient Resistance) characteristics and microstructure. The mixed powder was obtained from $BaCO_3$, $TiO_2$, $CeO_2$ ball-milled in attrition mill. The mixed powder was calcine from 1000 $^{\circ}C$ to 1200 $^{\circ}C$ in air and then it was sintered in reduction- re-oxidation atmosphere. As a result, The room-temperature electrical resistivity decreased and increased with increasing calcination temperature. specially, Attrition milled powder could have low room-temperature resistivity and high PTC jump order at 1100 $^{\circ}C$. attrition milling had lower room-temperature resistivity than ball milling. Particle size decreased by Attrition milling of powder influences in calcination temperature and room-temperature resistivity.

• Proceedings of the KIEE Conference
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• 1995.07a
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• pp.104-106
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• 1995

A curious resistivity anomaly in high curie point barium-lead-titanate materials with positive temerature coefficient of resistivity (PTCR) has been observed just below the curie point, besides the normal PTCR anomaly. The additional resistivity anomaly was observed in the resistivity-temperature characteristics.

• Journal of the Korean Chemical Society
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• v.39 no.10
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• pp.806-811
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• 1995

The electrical properties for $(Ba,Sr)_{1-x}Y_xTiO_3$(x=0.001∼0.009, BSYT) with a positive temperature coefficient of resistivity(PTCR) effect were investigated. The BSYT powder was prepared by oxalate coprecipitation method. It was found that the large PTCR effect was appeared up to 0.3 mol% and decreased above 0.5 mol% of the yttrium concentration. The plot of temperature vs. $1{\varepsilon}$m(T) above Curie temperature($T_c$) was agreed with Curie-Weiss law. The potential barrier calculated from measured resistivity and dielectric constant of specimens was high up to 0.3 mol% and reduced above 0.5 mol% of yttrium concentration as the curve of PTCR effect.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05d
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• pp.100-104
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• 2003

$BaTiO_3$ ceramic thin films were manufactured by rf/dc magnetron sputter technique. We have investigated crystal structure, surface morphology and PTCR(positive-temperature coefficient of resistance) characteristics of the specimen depending on second heat-treatment temperatures. Second heat treatments of the specimen were performed in the temperature range of 400 to $1350^{\circ}C$. X-ray diffraction patterns of $BaTiO_3$ thin films show that the specimen heat treated below $600^{\circ}C$ is an amorphous phase and the one heat treated above $1100^{\circ}C$ forms a poly-crystallization. In the specimen heat-treated at $1300^{\circ}C$, a lattice constant ratio (c/a) was 1.188. Scanning electron microscope(SEM) image of $BaTiO_3$ thin films of the specimen heat treated in between 900 and $1100^{\circ}C$ shows a grain growth. At $1100^{\circ}C$, the specimen stops grain-growing and becomes a poly-crystallization.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.7
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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 $200^{\circ}C/h$.