Charge Transport Mechanism Of Alkaline Earth Metal Ions Doped On Co-Mn-Ni-O Thermistor Materials

In the field of NTC thermistor research,the spinel-type transition metal oxide Co-Mn-Ni-O is widely used in the fields of temperature measurement and control,temperature compensation,and suppression of surge current due to its good performance.However,due to the wide application field of NTC,the measurement range is from 20 K to 1200 K.In view of the material system currently studied,it cannot be applied to all fields.Therefore,it is necessary to conduct regular research on the conduction mechanism of NTC thermosensitive material system.It can be applied to more fieldsIn this paper,Co-Mn-Ni-O system is used as the main body,and alkaline earth metals Ca,Mg,Sr and Ba are selected for doping experiments.The prepared powders and ceramics were analyzed and characterized by different preparation methods and different component ratios,combined with laser dynamometer,XRD,SEM,TG/DSC and electrical performance test.The main results are as follows:(1)Co_1.5Mn_1.2Ni_0.3O₄ powders were prepared by hydrothermal method.When the reaction conditions were 210°C and 8 h,the surface pore of the samples was the least,the grain growth was uniform,the compactness was the best,and the surface morphology of the samples was the best.When the sintering temperature is 1200°C,the grain size of Co_1.5Mn_1.2Ni_0.3O₄ ceramics sheet grows completely,and there are obvious grain boundaries and grains,and the density is the best.(2)Co_1.5-xCa_xMn_1.2Ni_0.3O₄(x=0,0.2,0.4,0.6,0.8)single-phase powder materials were prepared by hydrothermal method.The particle size of the powder gradually increased with the increase of doping amount.Reduced.When x=0.4,the grain growth is uniform,the compactness is the best,and the grain and grain boundaries are most obvious.Both the resistivity and the B value of the material decrease as the content of Ca increases.The resistivity?₂₅ and the material constant B_25/50,the activation energy Ea values vary from 1108.61?·cm to 416.17?·cm and 3804 K to3320 K,and 0.3282 e V to 0.2864 e V,respectively.(3)Co_1.5-xCa_xMn_1.2Ni_0.3O₄(x=0,0.2,0.4,0.6,0.8)single-phase powder materials were successfully prepared by traditional oxide solid phase method.As the Ca ion content increases,the diffraction peak shifts to a small angle.Both the resistivity and the B value of the material decrease as the content of Ca increases.The room temperature resistivity?₂₅,the material constant B_25/50,and the activation energy Ea range from 1291.5?·cm to 180.8?·cm,3860 K to 3077 K,and 0.333 e V to 0.2655e V,respectively.(4)Co_1.1M_0.4Mn_1.2Ni_0.3O₄(M=Mg,Ca,Sr,Ba)powders were prepared by traditional oxide solid phase method.The XRD analysis of the powders showed that a single spinel structure was formed.There is no second characteristic peak.As the atomic number increases,the diffraction peak moves toward a low angle.The surface SEM of Co_1.1M_0.4Mn_1.2Ni_0.3O₄(M=Mg,Ca,Sr,Ba)ceramic samples sintered at1200°C showed that Mg element and Sr element have the effect of improving the ceramic microstructure and increasing the uniformity of the ceramic.(5)The electrical properties of ceramics show that the material constant B value decreases first and then increases with the increase of atomic number in Co_1.1M_0.4Mn_1.2Ni_0.3O₄(M=Ca,Mg,Sr,Ba)ceramic materials.Trend,resistivity?₂₅exhibits a process of first decreasing and then increasing.The values of resistivity?₂₅,material constant B_25/50,and activation energy Ea range from 1206.7?·cm to 443.2?·cm,3881 K to 3521 K,and 0.3348 e V to 0.3038 e V,respectively.