Preparation And Stability Of NTC Thermistor With Low Resistivity And High B Value

Negative temperature coefficient thermistors(NTCR)are widely used in household appliances,temperature sensors and other fields because of their high sensitivity and low cost.With the rapid development of modern integrated circuits,the performance requirements for NTC thermistors are also increasing.In order to well suppress the surge current and protect the components in the electronic circuit,it is meaningful to prepare NTC thermistors with low resistivity,high B value and high stability.This article mainly uses Mn-Ni-Cu as the basic research system,with low resistivity,high B value and high stability as the research goals,and NTC thermistors are prepared by traditional solid-phase method.A series of studies have been carried out on the preparation process,doping elements and aging improvement.Firstly,the electronic structure and density of states of spinel NiMn₂O₄ before and after Cu doping were studied by the first principles.The calculation results show that the conductivity of the normal spinel NiMn₂O₄ before Cu doping is poor,while the conductivity of the inverse spinel NiMn₂O₄ after Cu doping is enhanced.Therefore,Conductivity of spinel NiMn₂O₄can be improved by Cu doping.Secondly,the sintering characteristics of the Mn-Ni-Cu material system were studied.The research results show that in the sintering temperature range of 1100?1200?,as the sintering temperature increases,the resistivity and B value both show U-shaped changes.The resistivity range is 15?100?·cm,and the B value range is 2300?3000K.When the sintering temperature is 1175?,the resistivity is 17.68?·cm,the B value is 2830K,and the aging rate is 11%.In order to improve its aging performance,the treatment process was adjusted and the effect of sensitization treatment on the performance of the Mn-Ni-Cu material system was studied.The results show that within the sensitization temperature range of 200?600?,the lattice structure of the material has not changed,it is the spinel structure,the resistivity range is 13?18?·cm,and the B value range is 2750?3300K.The sensitization temperature is 250°C and the minimum aging rate is 6%.In order to further reduce the aging rate,the effect of Zn doping on the performance of Mn-Ni-Cu material system was studied.The results show that in the range of 0?0.4 doping concentration,the resistivity of the material increases with the increase of doping.The resistivity range is15?60?·cm,and the B value range is 2800?3000K.When the concentration is 0.4,the aging rate is less than 2%after the sample is aged at 150?for 150h.Due to the excellent properties of Co in increasing the B value,Co was incorporated into Mn-Ni-Cu material and the sintering characteristics of the Mn-Ni-Co-Cu material was studied.The research results show that in the sintering temperature range of 1150?1200?,the resistivity range is 20?30?·cm,and the B value range is 2600?2900K.When the sintering temperature is 1175?,the resistivity is 15?·cm,the B value is 2900K,and the aging rate is 17.5%.In order to reduce the aging rate,the effects of Zn and Ca doping on the properties of the Mn-Ni-Co-Cu material system were studied respectively.The research results show that the resistivity of the material increases with the increase of Zn doping concentration in the range of 0.2?0.4,the resistivity range is 15?45?·cm,and the B value range is 3000?3300K.When the concentration is 0.3,the minimum aging rate is 5%;In terms of Ca doping,when the Zn doping concentration is 0.1?0.2,the resistivity of the material is 25?75?·cm,and the B value is 2800?3200K.When the Ca concentration is 0.15,the resistivity is 66?·cm,the B value is 3200K,and the aging rate is 6%.