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Wanju, South Korea

Jeong Y.H.,Korea Institute of Ceramic Engineering And Technology | Cha Y.-J.,Korea University | Kim C.-I.,Korea Institute of Ceramic Engineering And Technology | Lee Y.-J.,Korea Institute of Ceramic Engineering And Technology | And 4 more authors.
Applied Physics A: Materials Science and Processing | Year: 2012

The positive temperature coefficient of resistance (PTCR) characteristics of Na 2Ti 6O 13 (NT)-doped 0.94BaTiO 3-0.06(Bi 0.5Na 0.5)TiO 3 (BBNT) ceramics were investigated in order to evaluate the effect of NT as a new additive for lead-free PTCR thermistor application. The BBNT ceramic sintered at 1325°C exhibited a relatively high Curie temperature (T C ) of 158°C while its PTCR characteristic was not satisfactory for thermistor application. However, doping with NT significantly influenced the PTCR behavior of BBNT ceramic. It is considered that NT was responsible for grain growth of the BBNT by forming a liquid phase during sintering due to its low melting temperature of 1300°C. The grain growth resulted in the enhanced PTCR characteristics of BBNT ceramic. In particular, 0.1 mol% NT doped BBNT ceramic exhibited excellent PTCR performance of low resistivity at room temperature (1.6×10 2 Ω∈cm), resistivity increase near T C (1.28×10 4) and high T C of 158°C, suitable for lead-free PTCR thermistor application. © 2011 Springer-Verlag. Source


Cha Y.-J.,Korea Institute of Ceramic Engineering And Technology | Jeong Y.-H.,Korea Institute of Ceramic Engineering And Technology | Lee Y.-J.,Korea Institute of Ceramic Engineering And Technology | Paik J.-H.,Korea Institute of Ceramic Engineering And Technology | And 2 more authors.
Korean Journal of Materials Research | Year: 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 0.5Na 0.5)TiO 3 (BBNT-NT001) ceramics sintered at various temperatures from 1200°C to 1350°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°C, the specimen had a uniform microstructure with small grains. However, abnormally grown grains started to appear at 1250°C and a homogeneous microstructure with large grains was exhibited when the sintering temperature reached 1325°C. When the temperature exceeded 1325°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 0.5Na 0.5)TiO 3 ceramics by forming a liquid phase during the sintering at around 1300°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°C. The BBNT-NT001 ceramics had significantly decreased ñ rt and increased resistivity jump with increasing sintering temperature at from 1200°C to 1325°C. Especially, the BBNT-NT001 ceramics sintered at 1325°C exhibited superior PTCR characteristics of low resistivity at room temperature (122 Ω·cm), high resistivity jump (1.28 × 10 4), high resistivity temperature factor (20.4%/°C), and a high Tc of 157.9°C. Source


Jeong Y.H.,Korea Institute of Ceramic Engineering And Technology | Kim C.-M.,Korea Institute of Ceramic Engineering And Technology | Kim C.-M.,Yonsei University | Kim C.-I.,Korea Institute of Ceramic Engineering And Technology | And 5 more authors.
Journal of the Electrochemical Society | Year: 2011

0.95BaTiO3-0.05(Bi0.5Na0.5) Ti O 3 ceramics with a positive temperature coefficient of resistivity (PTCR) were fabricated by a modified synthesis process. Their structural and PTCR characteristics were investigated by varying the (Bi0.5 Na 0.5) TiO3-rich BaTi O3 (Bi0.5 Na0.5) Ti O3 intermediate composition in the additional step. For the specimen with the intermediate step composition of 0.94 (Bi 0.5 Na0.5) Ti O3-0.06BaTi O3, abnormally large grains grew with the aid of the liquid phase that developed due to the volatile Bi during sintering at 1300°C. Especially, it showed enhanced PTCR characteristics with a PTCR jump of 1.1× 104, temperature coefficient of resistivity of 41%/°C, and low resistivity at room temperature of 1.6× 102cm caused by its large grain boundary volume compared to the specimen fabricated by the normal synthesis process. © 2010 The Electrochemical Society. Source

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