Abstract The sintering behavior of nanocrystalline ZnO was investigated at only 250 °C. Densification was achieved by the combined effect of uniaxial pressure and the addition of water both in a Field Assisted Sintering Technology/Spark Plasma Sintering apparatus and a hand press with a heater holder. The final pure ZnO materials present high densities (>90% theoretical density) with nano-grain sizes. By measuring the shrinkage rate as a function of applied stress it was possible to identify the stress exponent related to the densification process. A value larger than one points to non-linear relationship going beyond single solid-state diffusion or liquid phase sintering. Only a low amount of water (1.7 wt%) was needed since the process is dictated by the adsorption on the surface of the ZnO particles. Part of the adsorbed water dissociates into H + and OH − ions, which diffuse into the ZnO crystal structure, generating grain boundaries/interfaces with high defect chemistry. As characterized by Kelvin Probe Force Microscopy, and supported by impedance spectroscopy, this highly defective grain boundary area presents much higher surface energy than the bulk. This highly defective grain boundary area with high potential reduces the activation energy of the atomic diffusion, leading to sinter the compound at low temperature.

中文翻译：

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通过改变外加应力和开尔文探针力显微镜表征晶界，揭示 ZnO 在 250 °C 冷烧结的机制

摘要 仅在 250 °C 下研究了纳米晶 ZnO 的烧结行为。在场辅助烧结技术/火花等离子烧结设备和带有加热器支架的手压机中，通过单轴压力和加水的综合作用实现致密化。最终的纯 ZnO 材料具有纳米晶粒尺寸的高密度（>90% 理论密度）。通过测量作为外加应力函数的收缩率，可以确定与致密化过程相关的应力指数。大于 1 的值表示非线性关系超出了单一固态扩散或液相烧结。只需要少量的水 (1.7 wt%)，因为该过程是由 ZnO 颗粒表面的吸附决定的。部分吸附水分解成 H + 和 OH - 离子，然后扩散到 ZnO 晶体结构中，产生具有高缺陷化学的晶界/界面。正如开尔文探针力显微镜所表征的那样，并得到阻抗谱的支持，这种高度缺陷的晶界区域呈现出比整体高得多的表面能。这种具有高电位的高度缺陷晶界区域降低了原子扩散的活化能，导致化合物在低温下烧结。