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http://dx.doi.org/10.3740/MRSK.2008.18.9.475

Lead-free BaTiO3-(Bi0.5K0.5)TiO3 PTCR Ceramics and Effects of Nb2O5 on Its PTCR Characteristics  

Jeong, Young-Hun (Korea Institute of Ceramic Engineering and Technology)
Park, Yong-Jun (Korea Institute of Ceramic Engineering and Technology)
Lee, Mi-Jae (Korea Institute of Ceramic Engineering and Technology)
Lee, Young-Jin (Korea Institute of Ceramic Engineering and Technology)
Paik, Jong-Hoo (Korea Institute of Ceramic Engineering and Technology)
Choi, Jin-Soo (Hiel Corporation)
Lee, Woo-Young (Hiel Corporation)
Publication Information
Korean Journal of Materials Research / v.18, no.9, 2008 , pp. 475-481 More about this Journal
Abstract
Positive temperature coefficient of resistivity (PTCR) characteristics of (1-x)$BaTiO_3-x(Bi_{0.5}K_{0.5})TiO_3$ ceramics doped with $Nb_2O_5$ were investigated in order to develop the Pb-free PTC thermistor available at high temperatures of > $120^{\circ}C$. The PTCR characteristics appearing in the ($B_{i0.5}K_{i0.5})TiO_3$ (< 5 mol%) incorporated $BaTiO_3$ ceramics, which might be mainly due to $Bi^{+3}$ ions substituting for $Ba^{+2}$ sites. The 0.99$BaTiO_3-0.01(Bi_{0.5}K_{0.5})TiO_3$ ceramics showed good PTCR characteristics of a low resistivity at room temperature (${\rho}_r$) of $31{\Omega}{\cdot}cm$ a high ${\rho}_{max}/{\rho}_{min}$ ratio of $5.38{\times}10^3$, and a high resistivity temperature factor (${\alpha}$) of $17.8%/^{\circ}C$. The addition of $Nb_2O_5$ to 0.99$BaTiO_3-0.01(Bi_{0.5}K_{0.5})TiO_3$ ceramics further improved the PTCR characteristics. Especially, 0.025 mol% $Nb_2O_5$ doped 0.99$BaTiO_3-0.01(Bi_{0.5}K_{0.5})TiO_3$ ceramics exhibited a significantly increased ${\rho}_{max}/{\rho}_{min}$ ratio of $8.7{\times}10^3$ and a high ${\alpha}$ of $18.6%/^{\circ}C$, along with a high $T_c$ of $148^{\circ}C$ despite a slightly increased ${\rho}_r$ of $31{\Omega}{\cdot}cm$.
Keywords
PTCR; $BaTiO_3$; Lead-free; $(Bi_{0.5}K_{0.5})TiO_3$; $Nb_2O_5$;
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