Preparation And Characterization Of Ni-Mn-O Negative Temperature Coefficient Thermistor Materials

The negative temperature coefficient thermistor (NTC) has advantageous of high sensitivity and stability, good reliability, heat fast response time and low cost. It is widely applied in many areas such as temperature test, temperature compensation and suppressing surge current. In order to meet miniaturization of NTC thermistor, it is very significant to develop NTC thermistor thin film. Basically, traditional approach for ma King thick film involving screen printing method would introduce the glass phase, resulting instability of electrical property. Thus, in this thesis, we propose to add additives containing Al and Zn into nickel manganite spinel by hydrothermal method. The phase, morphology and electrical properties of NTC thermistor materials were characterized by the X-ray diffraction (XRD), Scanning electron microscopy (SEM), and Transmission electron microscope (TEM). Moreover, Ni-Mn-Al-0 NTC thin film thermistors were directly prepared and the phase, morphology and electrical properties of the thin film were studied as well. The main results are as follows:1. Powered Ni-Mn-Al-0 has been prepared by the hydrothermal method. The effects of precursors, pH, and temperatures on the phase of composites were investigated by X-ray diffraction. It is found that the Ni-Mn-Al-0 prepared in acid (pH=5) with reaction temperature of 230℃ for 20 h and n[Mn(CH3COO)2]/n(KMnO4)=1:1 as well as NiMn2-xAlxO4 where x=0.2, showing single spinel phase. Further, the relationship between resistivity and temperature for compound indicated an NTC thermistor characteristic2. Powdered NiMn2-xAlxO4 has been prepared via hydrothermal method. The impact of precursors and hydrothermal synthesis conditions on the phase of composites were studied. Specifically, the NiMn2-xAlxO4 synthesized at temperature of 220℃ for 20 h and n[Mn(CH3COO)2]/n(KMnO4)=1:1 as well as NiMn2-xAlxO4 where x=1 showing single and stable spinel phase. Moreover, the relationship between resistivity and temperature for compound indicated an NTC thermistor characteristic.3. Ni-Mn-Al-0 thin film thermistors were directly prepared for the first time using Al2O3 as substrate through hydrothermal approach. The effects of precursors, hydrothermal conditions and substrate on crystal phase were studied. It is revealed that the single spinel NiMn1.8Al0.2O4 thin film can be obtained in acid (pH=5) at 230℃ for 20 h and n[Mn(CH3COO)2]/n(KMnO4)=1:1.Further, the relationship between resistivity and temperature for thin film indicated an NTC thermistor characteristic.