Solid solution range and oxygen diffusion of cerium oxide at low temperatures

在加热水溶液形成氧化铈固溶体的过程中，发现微波加热在特定条件下形成的颗粒与常规加热形成的颗粒不同。当这些颗粒在900℃下煅烧时，烧结样品的密度很高。经烧结和热处理后，用x射线衍射法测定了氧化铈固溶体的密度。掺Nd、Gd、Y的CeO_2在30%左右的浓度下固溶体呈萤石型结构，在较高浓度下固溶体呈稀土c型结构。随着这些掺杂剂的加入，CeO_2中晶格参数的变化取决于掺杂剂的种类：晶格参数连续增加（掺Nd的CeO_2），连续减少（掺Y的CeO_2），或先增加后减少（掺Gd的CeO_2）。这些固溶体的主要缺陷是萤石结构区域的阴离子空位。在稀土c型结构区中，掺Nd的CeO_2主要缺陷为阴离子空位，而掺y的CeO_2则转变为基于YO_<1.5>的阳离子空位。需要进一步的调查来证实这一点。在900 ~ 1400℃范围内，NdO_<1.5>在CeO_2中的溶解度较大。在较低温度下（500℃），在70% NdO_<1.5>时发现了两相区域的存在，表明溶解度对温度有轻微的依赖性。在400 ~ 550℃时，掺Nd的CeO_2中氧的扩散系数非常大，这是根据750℃以上的温度推断出来的。

In the process of forming cerium oxide solid solution by heating aqueous solution, it was found that particles formed by microwave heating at particular condition were different from those formed by conventional heating. It was also found that when these particles were calcined at 900℃, the density of sintered samples was high. After sintering and heat treatment, cerium oxide solid solutions were examined by x-ray diffraction and densities of them were measured. For CeO_2 doped with Nd, Gd, and Y, solid solutions were in fluorite structure in the concentration of about 30 % or less and they were in rare earth C-type structure in the higher concentration. As these dopants were added into CeO_2, the change in lattice parameter depended on the dopant species : the lattice parameter increased continuously (CeO_2 doped with Nd), decreased continuously (CeO_2 doped with Y), or first increased and then decreased (CeO_2 doped with Gd). The predominant defect in these solid solutions was anion vacancy for the region of fluorite structure. Although in the rare earth C-type structure region the predominant defect was anion vacancy for CeO_2 doped with Nd, it changed to cation vacancy based on YO_<1.5> for CeO_2 doped with Y. For CeO_2 doped with Gd, there was an indication that cation interstitial might be present at 10 % GdO_<1.5>. Further investigation is needed to confirm this. Solubility of NdO_<1.5> into CeO_2 was found to be large in the temperature range of 900-1400℃. At lower temperature (500℃) the existence of two-phase region was identified at 70 % NdO_<1.5>, suggesting a slight temperature dependence of solubility. The oxygen diffusion coefficient in CeO_2 doped with Nd at 400-550℃ was found to be very large and were on the line extrapolated from higher temperatures (750℃ or higher).