|Place of Conferral||北京|
|Keyword||Ntc 热敏电阻 微乳液法 尖晶石 陶瓷 晶粒电阻|
具有尖晶石结构的过渡金属氧化物是负温度系数(Negative Temperature Coefficient,NTC)热敏电阻的主要材料体系，其中以Mn-Co-Ni-O 基氧化物最为常见。MgO、Al2O3 是典型的耐高温氧化物,并且可以提高体系的室温电阻率和B 值，Fe2O3 也可以提高体系的电阻率，对体系B 值的影响则呈现“Ｕ”型变化。本文选择Mg、Al、Fe 共掺杂的Mn-Co-Ni-O 基NTC 热敏电阻为研究对象，采用微乳液法合成了纳米Mn1.05–yCo1.95–x–z–wNixMgyAlzFewO4 (0.03≤x≤0.15, 0.15≤y≤0.3, 0.03≤z≤0.42,0.3≤w≤0.45, 且x+y+z+w=0.9) NTC 热敏电阻粉体，通过优化水相中金属离子的沉淀工艺，使得粉体的最终组分与初始配比较为接近。并且研究了不同制备方法对体系结构及电性能的影响。红外吸收谱表明前驱粉体由草酸盐和氢氧化物组成，通过热分析(TG-DSC)得知前躯体的两次失重分别发生在272 ℃和307 ℃。从扫描电镜(SEM)和透射电镜(TEM)图像都可以看出所制备的粉体粒径在100 nm 以内。X 射线能量分散谱(EDS)表明粉体的化学组成与初始配比较为接近。通过X 射线衍射分析(XRD)技术得到粉体的最低烧结温度为600 ℃。通过对比发现，微乳液法制备的粉体其预烧温度比共沉淀法和固相法都要低，粒度分布也比后两者均匀。采用SEM、XRD 和光电子能谱分析(XPS)等方法分析了陶瓷的微观结构、锰元素价态等信息。从元素面分布图得知陶瓷体中元素分布较均匀。从1380 ℃烧结的样品到1450 ℃烧结的，晶粒尺寸迅速增大，再到1560 ℃烧结的，晶粒尺寸变化不大，但气孔率及气孔的尺寸却在增大，致密度则先增大后减小。当烧结温度相同时，微乳法制备的样品晶粒尺寸比共沉淀法和固相法都要大。X 射线衍射分析表明三个温度下烧结的样品都是以立方尖晶石相为主。对1450 ℃下烧结的陶瓷进行了电性能测试，其室温电阻率ρ25、材料常数B25/85 以及活化能Ea 分别在1173 Ω·cm -19059 Ω·cm, 3169 k -3771 k, 0.2672 eV-0.3136 eV 范围内。样品的室温电阻率ρ25 和材料常数B25/85 随着组分中Al2O3 含量的增加而增加；MgO 和Fe2O3 除了有与Al2O3 相同的机制增大体系的电阻率外，还会通过降低Mn3+的Jahn–Teller 效应以及增加电子在Mn3+/Mn4+离子对之间跳跃的距离来影响体系的电阻率和B 值。当组分和烧结温度相同时，相比于共沉淀法和固相法，微乳法制备的样品具有最小的室温电阻率ρ25、B25/85 值以及活化能Ea, 分别为2928 Ω·cm、3169 k、0.2672 eV。通过交流复阻抗分析知，在100 ℃到200 ℃范围内，陶瓷的负温度系数热敏电阻特性主要来自于晶界。
Transition metal oxides with spinel structure were good candidate for negative temperature coefficient (NTC) thermistor. Among those, the Mn-Co-Ni-O based oxide was the most common.MgO and Al2O3 were the typical high temperature resistant materials, which could also increase the resistivity and thermistor constant B of material. Fe2O3 could increase the resistivity of material, while the thermistor constant varied in “U” tendency. The Mg, Al and Fe co-doped Mn-Co-Ni-O series oxide was chosen to be studied. The Mn1.05–yCo1.95–x–z–wNixMgyAlzFewO4 (0.03≤x≤0.15, 0.15≤y≤0.3, 0.03≤z≤0.42, 0.3≤w≤0.45, and x+y+z+w=0.9) NTC thermistor nano-particle was synthesized by water in oil (W/O) inverse microemulsion. Powder with chemical component closely near to the initial composition was prepared by optimized reaction condition. The influence of preparation method on the microstructure and electrical properties of the material had also been discussed. Fourier infrared spectrometer indicated that the precursor was consisted of oxalate and hydroxide. Thermogravimetric–Differential scanning calorimetry (TG–DSC) curve showed that the twice weight losses of the precursor occurred at 272 ℃ and 307 ℃.Scanning electron microscope (SEM) and Transmission electron microscopy (TEM) image suggested that the particle size was within 100 nm. The chemical composition of the powder was investigated by X-ray energy dispersive spectrue (EDS). The most perfect calcination temperature (600 ℃) of the powder was obtained by the X–ray diffraction (XRD) techniche. The powder synthesized by microemulsion method possessed the lowest calcination temperature and the particle size distribution was the best compared with that synthesized by co-precipitation and solid state reaction methods. The grain size of the ceramics increased sharply when the sintering temperature increased from 1380 ℃ to 1450 ℃, and changed little when it further increased to 1560 ℃, while the porosity and pore size increased. The density increased firstly and decreased then. X–ray diffraction (XRD) pattern showed that the samples sintered at these three temperatures were all in cubic spinel structure. The ceramic showed greater grain size than that prepared by co-precipitation and solid state reaction methods at given sintering temperature. The room temperature resistivity ρ25, thermistor constant B25/85, and activity energies Ea of the ceramic sintered at 1450 ℃ were in the range of 3027-16911 Ω?cm, 3592-3977 K and 0.3112-0.3330 eV, respectively. The room temperature resistivity ρ25 and thermistor constant B25/85 were found to increase with the increasing Al2O3 content, in addition, MgO and Fe2O3 could also increase the room temperature resistivity ρ25 and thermistor constant B25/85 by reducing the Jahn-Teller effect of the Mn3+ and increasing the hoping distance for the charge carrier between the Mn3+/Mn4+ ion pair except for the mechanism as Al2O3. Compared with co-precipitation and solid state reaction methods, samples prepared by microemulsion method possessed the smallest room temperature resistivity ρ25, thermistor constant B25/85 and activity energies Ea of 2928 Ω?cm, 3169 k and 0.2672 eV, respectively. Complex impedance analysis indicated that the negative temperature coefficient thermistor characteristic of the ceramic was mainly derived from the grain boundary resistivity.
|夏军波. Mg、Al、Fe共掺杂的Mn-Co-Ni-O基NTC热敏电阻材料的制备与性能研究[D]. 北京. 中国科学院大学,2014.|
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