Semiconductive TiO_2 (rutile) ceramics were obtained in a conventional way. The effects of Nb_2O_5, SiO_2 doping contaminants on TiO_2 sintering and the electrical properties were investigated. It was found that Nb_2O_5 particles resist grain growth at 1350 ℃ when the form pressure of green pellet is less than 1100Kg/cm~2, and higher density is obtained when the pressure is higher than 1100Kg/cm~2 at 1350 ℃ or 800Kg/cm~2 at 1500 ℃. Grain growth was extremely retarded at 0.8 mole% Nb_2O_5 at 1400 ℃, whereas the densification was inhenced at 1500 ℃. The grain growth of Nb-doping TiO_2 follows (D-bar)_t~2-(D-bar)_o~2 = kt. At higher doping concentration, cation ions are rate controlling. After the third element SiO_2 was added, liquid sintering happened. In this case, the grain growth follows (D-bar)~3 ∝ kt. The resistivity decreases with increasing Nb-doping, but after the concentration is higher than 0.8 ～ 1.0mole%, it increases rapidly, which is maybe caused by second phases with low conductivity. The conductivity increases exponentially with increasing temperature. The activation energy of low doping specimen (≤1mole%) decreases slightly at temperature over 300℃, which is attributed to the scattering of pores containing O_2.
修改评论