Effect Of Doping On Spinel-type NTC Electrical Properties

NTCR(negative temperature coefficient thermistors)is widely used because of high stability,high sensitivity,good reliability and low prices. It has got more and more attention to doping on NTCR materials with corresponding required parameters and stable property at present.The Mn-Co-Ni series ceramics of NTCR materials with spinel were used as main materials in this paper,doped by oxide,using the traditional preparation of electronic ceramics,preparing a series of NTCR sample with spinel.Wirh measuring the value of the room temperature resistance of the above samples at a constant temperature environment,they were charactered by room temperature resistivityρ25 and material constant B-value,then the effect of doping on NTCR materials with spinel was analysed and discussed.First, it was systematically researched the effect of electrical property of doping-sole on NTCR materials with spinel in this paper,then it was founded that doping on NTCR materials by SiO₂ and Al₂O₃ can increase the value of room temperature(at 25℃)resistivity and material constant ,but excess doping was bad to the dense sintering of the NTCR materials with spinel,the best number of doping was about 1.0wt%;the doping of CuO can help sinter in the high temperature sintering as the fluxing medium,and the doping of Bi₂O₃ not only can reduce the sintering temperature ,but also contributed to the material constant B-value of NTCR ceramics.Secondly,in this paper,the effect of electrical property of doping on NTCR materials by Al₂O₃ and SiO₂ as well as ZnO,Al₂O₃ and TiO₂,the results showed that the contribution of material constant B-value by doping with Al₂O₃ was more than SiO₂.The doping on binary system material show that the room temperature resistivity was changed little and the B-value has changed widely.In the end,when sintered at 1200℃,mixed-doping of CuO,Al₂O₃,Bi₂O₃ and Fe₂O₃ on NTCR materials with spinel was founded that the room temperature resistivityρ25=550Ω·cm,and B-value was 3520K.