The Research Of Doped Mn-Co-O Negative Tempature Cofficient Thermistor Ceramics And Electrical Properties

In this paper, thermieter ceramic powders were prepared bycoprecipitation. The Mn-Co-O system is chosen for the matrix, thendoped with some kinds of metal ions, such as Zinc、Iron、Nickel and so on.The relationship among phase structure、 particle distribution andelectrical properties etc, are more studied. Moreover, the performances ofsamples influenced by development of technological conditions areresearched and an appropriate process conditions meeting the industrialproduction is studied as well. The main aspects in research are as follow:1. The amount of Mn or Co will impact the Mn-Co-O system and itsperformances in condition of Mn3-xCo_xO₄（0≤x≤3.0）. In this range, theresistance of material has a lower resistivity and a larger B value. In therange of1.2<x<1.8, the B value almost doesn’t change with the amount ofCo but keeps relatively stable. The electrical properties hardly shift withthe amount of Co and the resistivity is quite small, about1000Ω cm.2. Regarding Mn-Co-O system as the matrix to prepare Mn-Co-Fe-O system through oxalate coprecipitation. In condition that the amount of Co is invariable, the influences of the increase of Feon resistivity properties are studied. The results show that the phase structure can be affected by the amount of Co while Fe is very few in the system. As the amount of Fe increases gradually, thestructure of the system will form a pure spinel structure, and noother phase exists. As to the electrical properties of the system, inthe range of x<0.6, it has a lower resistivity and a larger B value. In general, the B value is taken on U-shaped.3. Mn-Co-Zn-O compounds are studied by doping Zn2+into theMn-Co-O system formed. The phase structure and electrical properties ofZn0.2Mn2.8-xCo_xO₄（0.7<x<2.3） series NTC ceramics are researched usingelectrical measurement and so on. With the increasing of Co content, the main phase of tetragonal spinel is firstly formed, and then a smallquantity of Co-rich rock salt phase separated out, it finally changed intocubic spinel main phase and rock salt phase. ρ25°C decreased rapidly first,and then increased slowly, while B value first decreased and then keptconstant between4400K and4500K, especially in the range of1.3<x<2.1,the samples has a lower resistivity and a higher B value.4. The impact on the physical properties， phase structure and micr-structure of Mn-Co-Ni-O system through the change of the solvent andthe sintered process are studied. The results show that while the ratio ofsolvent is1:1, particle size reduces significantly. When the lower sinteredtemperature is1150°C, the sintering activity of powder increased and thephase structure was a pure spinel but no other phase existed. According tothe EDS graph, the proportion of elements is closed to the nominalcompose. It provides some guidance for industrial production.