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题名: 稀土掺杂Mn-Ni-Cu-O系NTC热敏材料制备制备及低温电学性能研究
作者: 姚金城
答辩日期: 2014-05-28
导师: 常爱民
专业: 微电子学与固体电子学
授予单位: 中国科学院大学
授予地点: 北京
学位: 博士
关键词: 热敏电阻 ; 尖晶石 ; 钙钛矿 ; 稀土掺杂 ; 阻抗分析
摘要: 随着科技的快速发展,特别是空间技术的发展,对热敏电阻器除了要求高可靠、长寿命、灵敏度高,还需要适用于高温和低温环境。由于低温领域的特殊性以及相关技术的复杂性,增加了人们对低温温度的获得和准确测量的难度,低温温度传感器作为一门极端技术,得到各国的普遍重视。低温热敏材料是低温温度传感器的核心,热敏材料的性能决定了温度传感器的性能和应用领域。适用于低温环境的热敏材料的研制开发具有重要的工程应用价值。由于Mn-Ni-Cu-O 系氧化物陶瓷材料因具有较低的电阻率而得到广泛的关注,材料的电阻率一般随Cu 含量的增加而减小,但Cu 含量的增加使材料的稳定性及器件的可制造性降低。而钙钛矿稀土锰氧化物具有较低的电阻率和较高的化学稳定性,越来越受到人们的关注与重视。因此,本论文以具有尖晶石结构的Mn-Ni-Cu-O 过渡金属氧化物热敏陶瓷为研究对象,以稀土氧化物为掺杂剂,使稀土氧化物和过渡金属氧化物通过物理混合,高温烧结形成尖晶石相与钙钛矿相共存的复合陶瓷材料。主要通过X 射线衍射(XRD)和扫描电子显微镜(SEM)分析表征陶瓷材料的晶型结构、微观结构组织均匀性及晶粒与晶界分布规律;通过电阻温度特性测试表征其电性能随温度变化规律、复阻抗特性分析表征材料内部导电机制、X 射线光电子能谱仪(XPS)对陶瓷材料离子价态进行探讨,从而获得热敏陶瓷材料微观组织结构与电学性能之间的关系,达到用稀土掺杂调整陶瓷材料的电阻率、提高陶瓷材料的稳定性的目的。研究内容主要包括以下几点:1)采用固相反应法制备了Mn0.75Ni1.25CuO4+xLa2O3(0≤x≤0.3)热敏陶瓷材料,通过XPS 测试,考察其阳离子价态分布情况,经分峰拟合发现存在Cu2+和Cu+、Mn3+和Mn4+ 两种异价离子同时存在。我们推断该热敏陶瓷材料的电导机制主要有两种,一种是尖晶石结构的小极化子电导机制,主要包括近邻八面体中心的 Mn4+和 Mn3+阳离子之间的跳跃: Mn Mn Mn4 Mn3 以及次近邻八面体中心的Cu2+ 和Cu+ 、Mn4+ 和Mn3+ 阳离子之间的跳跃: Mn Cu Mn  Mn Cu Mn  Mn4  Cu2 Mn3,另一种是钙钛矿结构中的双交换电导机制。LaMnO3 钙钛矿结构中的电子从一个Mn 离子通过O2-离子转移到另一个 Mn 离子的双交换导电机制:Mn3+—O2-—Mn4+eMn4+—O2—Mn3+。这种双交换电导机制很好的解释了随着La2O3 添加量的增加,也就是钙钛矿相比重的增加,对复合热敏陶瓷材料起增大阻值的作用,可以通过调节钙钛矿结构的比重来调节材料的阻值,满足低温应用的要求。2)采用固相反应法合成的Mn0.75Ni1.25CuO4+xYb2O3(0≤x≤0.3)热敏陶瓷材料,经SEM 分析表明该陶瓷材料微观结构随着镱锰钙钛矿相增加,陶瓷材料晶粒变小,产生的气孔先增加后减少。这可能是由于镱锰钙钛矿相的生成抑制了尖晶石结构的生长,同时,晶粒尺寸的减小和晶粒间有效接触面积的减小增加了气孔数量。通过陶瓷材料Mn0.75Ni1.25CuO4+xYb2O3(0≤x≤0.3)阻值与温度变化关系可以发现电阻值随温度的升高呈指数关系降低,这是一种典型的负温度系数热敏行为。通过伏安特性,可知施加电流较小时,热敏陶瓷的电压随电流呈线性变化,符合欧姆定律。当电流足够大时,电压达到了峰值,在同一温度下,随Yb2O3 掺杂量的增加,这一峰值逐渐增大,耗散系数增加。3)用固相反应法制备了Fe 和La 共同掺杂Mn0.75NiCuO4 热敏陶瓷材料。通过XRD 和XPS 分析结果发现Fe 和La 元素的存在不会改变尖晶石结构的晶相组成和化学价态作用,铁元素的增加主要进入尖晶石结构,阻碍了八面体中心的Mn4+和Mn3+阳离子之间的跳跃,极大的增加了陶瓷材料的电阻率,而不会影响材料的导电机制。在30K~44K 温度范围内, 热敏陶瓷材料Mn0.75NiCuFe0.25O4+xLa2O3(x=0,0.05)具有明显的负温度系数特性,电阻率ρ30K分别为5806 Ω·cm 和6337 Ω·cm,材料常数B30/40 值分别为197 K 和184K。而当x=0.1 和0.2 时的电阻率超出仪器测试量程。在70K 时,电阻率分别为9416 Ω·cm和11376 Ω·cm,材料常数B70/80 值分别为568 K 和609 K。因此可以通过Fe 和La 共掺较大幅度提高陶瓷材料的阻值和B 值,扩展热敏电阻材料的应用范围。4)将钙钛矿结构材料LaMnO3 与尖晶石结构材料Mn0.75Ni1.25CuO4 相结合合成复合热敏陶瓷材料Mn0.75Ni1.25CuO4+x(wt.%)LaMnO3。经XRD 结果表明主要由立方尖晶石相、富镍盐岩相、氧化铜相和钙钛矿相镧锰氧结构组成。正如预料,LaMnO3 的加入并没有影响原来的尖晶石结构,而是保持了原来的钙钛矿相
LaMnO3。LaMnO3 的增加在微观形貌上表现为球状细小颗粒的增多,在电学性能上表现为热敏陶瓷材料的ρ30K 随着LaMnO3 含量的增加而增大,材料常数B 值、激活能Ea 变化较小。因此,通过控制引入LaMnO3 的比例,可调整陶瓷材料的电学性能,拓宽热敏陶瓷材料Mn0.75Ni1.25CuO4+x(wt.%)LaMnO3 的使用范围。
英文摘要: With the rapid development of technology, especially the development of space technology, thermistors need not only high reliability, long life, high sensitivity, but also applying in high temperature and low temperature environments. Due to the particularity and complexity in low-temperature areas, the cryogenic temperature sensor has been attracting people's universal attention, as to obtain accurate temperature measurement. The core material of temperature sensor is a low-temperature thermistor, which determines the performance and application of the temperature sensor. It has important application value for low temperature thermal material with a low thermal resistance and low material constants. It has the widespread concern with the a lower resistivity of Mn-Ni-Cu-O-based oxide ceramic material. The resistivity generally decreases the content of Cu increases, the Cu content is increased but the stability of the material and device manufacturability reduced. The rare earth perovskite manganese oxide is a typical strongly correlated electron systems, novel electron transport and spin transport properties, with a low resistivity. In this study, rare earth oxides and transition metal oxides were doped to the Mn-Ni-Cu-O based NTC ceramics to develop high-performance. X ray diffraction (XRD) and Scanning electron microscope (SEM) were applied to analyze crystal structure, distribution of grain boundary and grain. Resistance temperature properties test instrument is characteristic of its electrical performance variation with temperature, and complex impedance analyzer for materials characterization the internal conductive mechanism, as well as using X ray photoelectron spectroscopy (XPS) to carry on the discussion to the ceramic material ion valence. Thus, it will btain the interaction between the microstructure and electrical properties of ceramics to improve the resistivity and stability. 1) The thermal ceramic materials Mn0.75Ni1.25CuO4 + xLa2O3 (0 ≤ x ≤ 0.3) were prepared by solid-phase reaction. There were two dissimilar valence states Cu2+ and Cu+, Mn3+ and Mn4+ ions by XPS test. Thus, we conclude that the mechanism of the thermal conductivity of ceramic materials have two main forms, one is small polaron conduction mechanism in spinel structure, including neighbor octahedral centers between: Mn4+ and Mn3+ cations and the next nearest neighbor octahedral center Mn4+ and Mn3+ cations: . The other is a double exchange mechanism in perovskite. Electron transfer of the double exchange from a Mn ions into another Mn ion by O2-ions: Mn3+—O2-—Mn4+ Mn4+—O2-—Mn3+. This double exchange mechanism is well explained in the conductance. With increasing addition of La2O3, the role of the thermal resistance of ceramic materials was increased. So these materials can adjust the resistance of materials to meet the requirements of low-temperature applications. 2) The SEM analysis of ceramic materials Mn0.75Ni1.25CuO4 + xYb2O3 (0 ≤ x ≤ 0.3) showed that with the increasing of ytterbium manganese perovskite phase small pores of grain ceramic material were produced decrease after the first increase. This may be due to ytterbium manganese perovskite phase for inhibiting the growth of a spinel structure. And the effective contact area of the number of pores was increased by reducting the grains and the ion of grain size. In the relationship between the resistance and temperature of ceramic materials Mn0.75Ni1.25CuO4 + xYb2O3 (0 ≤ x ≤ 0.3) can be found is decreasing exponential relationship, which is a typical negative temperature coefficient thermistor behavior. Through the volt-ampere characteristics, we can see the voltage applied on the ceramic varies linearly with the current at a small current, which comply with the Ohm's law. When the current is large enough, the voltage reaches the peak at the same temperature, with the increase of the doping amount of Yb2O3, the peak value increases, the dissipation factor increased. 3) Fe and La co-doped Mn0.75NiCuO4 thermal ceramic material were prepared by solid state reaction. It revealed the presence of La and Fe elements did not change the crystal structure of the spinel phase composition and chemical valence effect. The introduction of Fe into the spinel structure is mainly hampered octahedral centers Mn4+ and Mn3+ cation between jumps, greatly increasing the resistivity of the ceramic material, without affecting the conduction mechanism of the material. In the 30K ~ 44K temperature range, thermal ceramic materials Mn0.75NiCuFe0.25O4 + xLa2O3 (x = 0, 0.05) has a significant negative temperature coefficient, the electrical resistivity ρ30K was 5806Ω?cm and 6337 Ω?cm, respectively, material constant B30/40 values were 197 K and 184 K. The resistivity of the Mn0.75NiCuFe0.25O4 + xLa2O3 (x = 0.1, 0.2) were not measured since the devices beyond the test range. In the 70K, the resistivity and material constant B70/80 values were 9416 Ω?cm and 11376 Ω?cm, 568 K and 609 K, respectively. So the resistance and B value of Mn0.75NiCuFe0.25O4 + xLa2O3 thermal ceramic material were increased, which can expand the application field of thermistor ceramic materials. 4) Ceramic materials Mn0.75Ni1.25CuO4+x(wt.%)LaMnO3 were synthesiszed by LaMnO3 perovskite structure and spinel structure Mn0.75Ni1.25CuO4. It showed that the main phase of cubic spinel structure, Ni-rich rock-salt phase, oxidation copper phase and lanthanum manganese oxide perovskite phase structure by XRD results. As expected, the addition of LaMnO3 did not affect the original spinel structure, but kept the formation of perovskite phase LaMnO3. With the increase of LaMnO3, the performance of the spherical fine particles increases and the resistivity ρ30K increases with small changes of the material constant B value and activation energy Ea. Thus, by controlling the ratio of introduction of LaMnO3, we can adjust the electrical properties of Mn0.75Ni1.25CuO4 + x (wt.%) LaMnO3 ceramic materials, to broaden the application scopes. Key words: Thermistor, Spinel, Perovskite, Rare earth doping, Impedance analysis
内容类型: 学位论文
URI标识: http://ir.xjipc.cas.cn/handle/365002/3418
Appears in Collections:材料物理与化学研究室_学位论文

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作者单位: 中国科学院新疆理化技术研究所

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姚金城. 稀土掺杂Mn-Ni-Cu-O系NTC热敏材料制备制备及低温电学性能研究[D]. 北京. 中国科学院大学. 2014.
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