|Place of Conferral||北京|
|Keyword||Ntc复合陶瓷电阻 钙钛矿相 电性能 导电机理|
NTC热敏电阻材料稳定性好、灵敏度高、价格低廉，广泛应用于温度测量与控制、抑制浪涌电流及温度补偿等领域。目前，实际用于宽温区的NTC热敏电阻还较少。太空中背光和向光连续测温等领域对宽温区NTC热敏电阻有广泛地需求，并且对稳定性有着很高的要求，因此需研究具有高稳定性的宽温区NTC热敏电阻。LaCrO3是一类典型的钙钛矿结构的材料，具有高的电学稳定性、热稳定性、化学稳定性和结构稳定性等特点。该材料可作为潜在的热敏陶瓷材料，这主要是由于该材料A、B位阳离子的稳定分布、不易重排，显示出极高的稳定性。但其在较高温时，电阻率较低无法使用。本文以LaCrO3为基体材料，通过离子取代和复合高阻相材料对其电性能进行了改进。使用高温固相法和低热固相法制备了La1-xBaxCrO3（x=0~0.2），研究了Ba2+对材料电性能等的影响；并探究了低热固相法中不同铬盐水合物对LaCrO3陶瓷制备的影响。YSZ材料具有化学性质稳定、耐腐蚀、高阻值等特征，因此制备了以YSZ为“核”、La0.8Ba0.2CrO3为“壳”具有“包覆结构”NTC热敏电阻，研究了不同“核”尺寸对NTC热敏电阻电性能的影响。随后以LaCrO3与YSZ复合，研究复合材料的复合度对陶瓷结构及电性能的影响；并研究了0.2LaCrO3-0.8YSZ在不同温度点的复阻抗，探究其导电机理。主要研究结果如下：（1）高温固相法制备了La1-xBaxCrO3（x=0~0.2）陶瓷材料，陶瓷样品均形成单一与LaCrO3同构的正交钙钛矿相。随着Ba掺杂量的增加，陶瓷样品逐渐变得致密。掺杂Ba形成了Ba-Cr-O的液相烧结，增强了其烧结活性。La1-xBaxCrO3陶瓷样品的电阻率随着温度的升高而降低，且具有良好的NTC特性。随着Ba掺杂量的增加，La1-xBaxCrO3陶瓷样品的电阻率逐渐减小。XPS表明随Ba2+离子掺杂量的增加，提高了Cr6+离子的浓度，说明Cr6+离子浓度是影响材料电阻率的主要因素。La1-xBaxCrO3陶瓷样品的自然对数(lnρ)与绝对温度倒数(1000/T)具有线性关系，该陶瓷导电机理符合小极子跳跃导电，其电导主要是Cr3+与Cr6+之间传输。陶瓷样品的ρ-50 (Ω·cm)、B-25/-50 (K)和Ea (eV)变化范围分别为：49.278–1.9839×105 Ω·cm、1767.4–3496.9 K和0.1523–0.3013 eV。（2）低热固相法制备了La1-xBaxCrO3（x=0~0.2）陶瓷材料，研究发现以La(NO3)3·6H2O 和Cr(NO3)3·9H2O为原料制备的LaCrO3粉体比以La(NO3)3·6H2O 和CrCl3·6H2O为原料制备的粉体更为均匀、细小，且LaCrO3陶瓷片的致密性更好，这是由于Cr离子配位的离子不同。制备的La1-xBaxCrO3（x=0~0.2）陶瓷样品，当Ba掺杂量为0.2时，陶瓷样品相结构中有杂相析出。陶瓷体的ρ-50、B-25/-50变化范围为177.1–16118.9Ω·cm、1876.4–3188.7K。（3）La1-xBaxCrO3-YSZ“包覆结构”陶瓷具有高阻、低B特性。通过调节内“核”YSZ的尺寸，实现陶瓷片阻值的调节，但其B值不变。在高温下，内部“核”YSZ与外部壳“La1-xBaxCrO3”界面连接处发生了反应，生成了BaZrO3。La1-xBaxCrO3-YSZ“包覆结构”陶瓷在测试温区-198℃~75℃内具有良好的NTC特性。陶瓷样品的R-50变化范围为13.52–418.88Ω，B-25/-50 范围为1682–2167K。（4）xLaCrO3-(1-x)YSZ复合陶瓷相结构仅存在LaCrO3的钙钛矿相与YSZ相；当LaCrO3与YSZ摩尔比为2：8时，复合陶瓷体致密度最好，EDS表明两相材料均匀分布。随着YSZ复合比例的增加，复合陶瓷的电阻率成倍增加，其B值变化较小，具有高阻、低B的特性。在25℃时，复合陶瓷的电阻率范围为：424.8–9.119678×105 Ω·cm；B0/25值的范围为：3252.5–3684.9 K。0.2LaCrO3-0.8YSZ的复合陶瓷体在-50℃~600℃温区间内具有良好的NTC特性。在500℃时，ρ500=3.561×103 Ω·cm， B400/500=3710.2 K。0.2LaCrO3-0.8YSZ的复合陶瓷的复阻抗表明，其NTC特性主要是来源于晶界电阻，晶粒电阻几乎不随温度变化。
NTC thermistor materials have good stability, high sensitivity and low price, so they are widely used in the fields of temperature measurement and control, suppression of inrush current and temperature compensation. At present, there are few NTC thermistors that can be used in wide temperature regions. The continuous temperature measurement of backlight and surface to light in the space, there are wide demand for NTC thermistors in wide temperature range, and high requirements for stability. Therefore, it is necessary to explore new NTC thermistor materials with wide temperature area. The LaCrO3 is a typical material of perovskite structure with high electrical stability, thermal stability, chemical stability and structural stability. Because the cations A and B of the LaCrO3 is stable distribution and show very high stability during aging, it can be used as a potential thermistor material. At higher temperature, the lower resistivity limit its application. In this paper, all ceramics based on the LaCrO3 system and its electrical properties were improved by ion substitution and compounding with high-resistance phase materials. La1-xBaxCrO3(x=0~0.2) was prepared by traditional solid-state reaction and low heat solid-state reaction. The effect of different Chromate compounds on preparing LaCrO3 ceramics was investigated in the low-heat solid-state reaction. The YSZ materials are characterized by chemical stability, corrosion resistance and high resistance. The NTC thermistor with “coated structure” which the YSZ as core and La0.8Ba0.2CrO3 as shell was prepared. The electrical properties of NTC thermistor was studied. Then the LaCrO3 were compounded with YSZ to study the relationship of the complex degree, structure and electrical properties of the ceramics. The complex impedance of 0.2LaCrO3-0.8YSZ at different temperature points was also investigated, and the conductive mechanism was explored. The main results are shown:(1) La1-xBaxCrO3 (x=0~0.2) ceramic samples were prepared by traditional solid-state reaction. All the samples of ceramics were consisted of a single phase isomorphic to the orthorhombic perovskite LaCrO3. As the doping amount of Ba increases, the ceramic samples gradually become dense. With doping of Ba2+, the samples will form liquid-phase sintering of Ba-Cr-O, which increses the sintering activity. The resistivity of La1-xBaxCrO3 ceramic samples decreases with increasing temperature and has good NTC characteristics. With the increase of Ba2+, the electrical resistivity of La1-xBaxCrO3 ceramics gradually decreases. The XPS shows that, the concentration of Cr6+ is increased with the increase of Ba2+. It indicates that the concentration of Cr6+ is the main reason on the resistivity of La1-xBaxCrO3 ceramic samples. The natural logarithm (lnρ) of the La1-xBaxCrO3 ceramic sample has a linear relationship with the reciprocal of the absolute temperature (1000/T). The conductive mechanism of this ceramic conforms to the small pole hopping conduction, and its conductance is mainly transmitted between Cr3+ and Cr6+. The range of ρ-50 (Ω·cm), B-25/-50 (K), and Ea (eV) are 49.278–1.9839×105 Ω·cm, 1767.4– 3496.9 K and 0.1523–0.3013 eV, respectively.(2) For ceramic samples prepared by low-heat solid-state reaction, the LaCrO3 powders prepared with La(NO3)3·6H2O and Cr(NO3)3·9H2O are more uniform and finer than the powders prepared with La(NO3)3·6H2O and CrCl3·6H2O, better densification of LaCrO3 ceramic, due to the different ions coordinated by Cr ions. For the La1-xBaxCrO3 (x=0~0.2) ceramic samples prepared, when the doping amount of Ba is 0.2, the heterophase generates in the phase structure of the ceramic sample. The ρ-50 and B-25/-50 values range from 177.1 to 16118.9 Ω·cm and 1876.4 to 3188.7K.(3) The La1-xBaxCrO3-YSZ ceramics with “coated structure” have high resistance and low B. The resistance of the ceramic can be adjusted by adjusting the size of the “core” YSZ but the B value of ceramic don’t change. At high temperatures, the “core” YSZ reacts with the shell “La1-xBaxCrO3” interface where BaZrO3 is formed. The La1-xBaxCrO3-YSZ ceramics with “coating structure” have good NTC characteristics in the temperature range of -198°C～75°C. The range of R-50 and B-25/-50 are 13.52-418.88Ω and 1682-2167K, respectively.(4) Only the phase of LaCrO3 and YSZ exist in the phase structure of xLaCrO3-(1-x)YSZ composite ceramics. When the molar ratio of LaCrO3 to YSZ is 2:8, the density of the composite ceramics is the best, and EDS shows that the two-phase composites are evenly distributed. With the increasing of the YSZ, the resistivity of the composite ceramic increases exponentially, but its B value changes little, so it possesses characteristics of high resistance and low B value. At 25°C, the resistivity of the composite ceramics ranges from 424.8–9.119678×105 Ω·cm and the B0/25 value ranges from 3252.5–3684.9 K. The 0.2LaCrO3-0.8YSZ composite ceramic possesses excellent NTC characteristic in the temperature range of -50～600°C. At 500°C, ρ500 = 3.561x103 Ω·cm, B400/500 = 3710.2 K. The complex impedance of the 0.2LaCrO3-0.8YSZ composite ceramic shows that the NTC characteristic is mainly due to resistance of grain boundary, and grain resistance does not change with temperature.
|陈明星. La1-xBaxCrO3-YSZ复合陶瓷的构筑及热敏特性研究[D]. 北京. 中国科学院大学,2018.|
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