Preparation And Electrical Properties Study Of Ce And Zr Ion Doped Ca₂Nb₂O₇ Thermo-sensitive Ceramics

Negative temperature coefficient（NTC）thermistors play an important role in temperature monitoring and control.Traditional spinel type NTC ceramics operating at or above 300℃ will produce resistance drift due to the redistribution of cations occurs in ceramics.However,the thermistor must maintain good stability in the extreme environment of automotive,medical,aerospace and other fields,so the research on high temperature NTC thermistor is of great significance.Ca₂Nb₂O₇ has high curie temperature and NTC characteristics in a specific temperature range.But its resistance is too large,so it needs to be doped ions to improve its electrical properties and high temperature stability.The main results are as follows:（1）Ca_2-xCe_xNb₂O₇（x=0,0.05,0.15,0.25）ceramics were prepared by traditional solid-state method.The grain size of the doped ceramics increased slightly.These ceramics have obvious NTC properties at 400-1200℃.The ranges ofρ₉₀₀、ρ₁₁₀₀、B_900/1100、α₉₀₀、α₁₁₀₀、Ea_900/1100of Ca_2-xCe_xNb₂O₇ ceramics are 9.21×10³～3.82×10⁴?cm、903～3.90×10³?cm、-0.0136～-0.0127K^-1、-0.0103～-0.0093 K^-1、17474～18682 K、1.51～1.61 e V,respectively.The results show that theΔR₁/R₀ of ceramic pre-aging at 1000℃for 200 h are 10.93～33.06%.After aging at 1000℃for300 h,theΔR₂/R₁ of ceramic are 1.23%～6.81%.These ceramics has excellent high temperature stability.（2）CaCeZrNbO₇ pyrochlore-type NTC thermistor were successfully prepared by traditional solid phase method,but a large amount of CeO₂ was found to precipitate in the ceramics.The preparation of Ca Ce Zr NbO₇powder was optimized.The Ca Ce Zr NbO₇ powder was prepared by the method of powder of composite ceramic.It was found that the ceramic was pure Ca Ce Zr NbO₇phase after sintering,and no second phase was formed.Pure phase Ca Ce Zr NbO₇ has obvious NTC properties at 300～1100℃.The two-step sintering method was used to prepare Ca Ce Zr NbO₇ceramics.It was found that the dense Ca Ce Zr NbO₇ ceramics could be obtained at 1300℃.Compared with the conventional sintered ceramics,the resistivity of these ceramics decreased.The electrical parametersρ₉₀₀、ρ₁₁₀₀、B_900/1100、α₉₀₀、α₁₁₀₀、Ea_900/1100of ceramics are 2383?cm、284?cm、12155 K、-0.0128 K^-1、-0.0088 K^-1、1.01e V,respectively。（3）(Ca_1-xCe_x)₂(Zr_xNb_1-x)₂O₇（x=0,0.05,0.25,0.5,0.75）ceramics were prepared by traditional solid state method.It has obvious NTC characteristics at 300-1100℃.The ranges ofρ700、ρ900、B700/900、α700、α900 and Ea700/900 of（Ca1-x Cex）2（Zrx Nb1-x）2O7 ceramics are 604～1.24×10⁶?cm、48～3.95×10⁴?cm、-0.0232～-0.0107 K^-1、-0.0143～-0.0073 K^-1、10106～19693 K、0.87～1.70 e V,respectively.The composite of Ca Ce Zr NbO₇ and Ca₂Nb₂O₇ can reduce the resistivity and B value.After aging at 700℃for 200 h,ΔR₁/R₀ of the ceramics are 1.38～15.42%.After aging at700℃for 300 h,it is found thatΔR₂/R₁ of pure Ca₂Nb₂O₇ ceramics is 2.67%,andΔR₂/R₁ of the doped ceramics are less than 1%.In addition,compared with Ce-doped Ca₂Nb₂O₇ ceramics,these ceramics have better high temperature stability.