Materials Science, California Institute of Technology, 1200 E. California Blvd. Pasadena, California 91125, USA.
Phys Chem Chem Phys. 2011 Apr 14;13(14):6442-51. doi: 10.1039/c0cp02198a. Epub 2011 Mar 8.
The impact of hydration on the transport properties of microcrystalline Sm(0.15)Ce(0.85)O(1.925) has been examined. Dense, polycrystalline samples were obtained by conventional ceramic processing and the grain boundary regions were found, by high resolution transmission electron microscopy, to be free of impurity phases. Impedance spectroscopy measurements were performed over the temperature range 250 to 650 °C under dry, H(2)O-saturated, and D(2)O-saturated synthetic air; and over the temperature range 575 to 650 °C under H(2)-H(2)O atmospheres. Under oxidizing conditions humidification by either H(2)O or D(2)O caused a substantial increase in the grain boundary resistivity, while leaving the bulk (or grain interior) properties unchanged. This unusual behavior, which was found to be both reversible and reproducible, is interpreted in terms of the space-charge model, which adequately explains all the features of the measured data. It is found that the space-charge potential increases by 5-7 mV under humidification, in turn, exacerbating oxygen vacancy depletion in the space-charge regions and leading to the observed reduction in grain boundary conductivity. It is proposed that the heightened space-charge potential reflects a change in the relative energetics of vacancy creation in the bulk and at the grain boundary interfaces as a result of water uptake into the grain boundary core. Negligible bulk water uptake is detected under both oxidizing and reducing conditions.
已经研究了水合作用对微晶 Sm(0.15)Ce(0.85)O(1.925)输运性能的影响。通过传统陶瓷加工获得了致密的多晶样品，并通过高分辨率透射电子显微镜发现晶界区域没有杂质相。在 250 至 650°C 的温度范围内，在干燥、H(2)O 饱和和 D(2)O 饱和的合成空气中以及在 575 至 650°C 的温度范围内在 H(2)-H(2)O 气氛下进行了阻抗谱测量。在氧化条件下，H(2)O 或 D(2)O 的加湿导致晶界电阻率显著增加，而体相（或晶粒内部）性质不变。这种不寻常的行为被发现是可逆和可重复的，它是根据空间电荷模型来解释的，该模型充分解释了测量数据的所有特征。结果发现，加湿时空间电荷势增加了 5-7mV，这反过来又加剧了空间电荷区中氧空位的耗尽，导致观察到的晶界电导率降低。据推测，空间电荷势的升高反映了由于水进入晶界核心，在体相和晶界界面处空位形成的相对能量发生变化。在氧化和还原条件下，都检测到几乎没有体相水分的吸收。
