Structural Disorder in the Anion Lattice of Nanocrystalline Zirconia and Hafnia Particles
Structural Disorder in the Anion Lattice of Nanocrystalline Zirconia and Hafnia Particles
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纳米晶氧化锆和氧化铪颗粒阴离子晶格的结构紊乱
DOI：
10.1557/proc-634-b7.7.1
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发表时间：
2000
期刊：
影响因子：
--
通讯作者：
D. Szabó
中科院分区：
文献类型：
--
作者：
D. Vollath;M. Forker;M. Hagelstein;D. Szabó
尺寸约为5 nm的ZrO 2和HfO 2纳米颗粒-取决于生产路线-以立方或四方或单斜相存在。为了阐明这种差异，对通过微波等离子体工艺制备的氧化铝涂覆的纳米颗粒进行了晶体结构、距离和围绕阳离子的对称性的分析。在准确度范围内，电子衍射和显微镜揭示了这两种材料的可能的立方阳离子晶格。在ZrO 2的情况下，来自扩展的X射线吸收精细结构（EXAFS）数据的修改后的径向分布函数的振幅的评估导致的结构与邻居的第一壳层中的氧离子的窄分布。这是立方结构的预期结果。将虚部与模型计算结果相比较，与立方结构有明显的相似性。在第二层的邻居，由金属离子，一个径向分布峰预计和实验发现。扰动角相关测量表明金属离子的第一邻居的位置的一个明显的障碍。再加上EXAFS观测到的第一近邻氧离子的窄径向分布，这些测量提供了证据的随机分布的Zr-O键角在其晶体位置附近。在500°C以上，观察到部分可逆的转变为几乎完美的四轴对称。因此，人们不得不得出结论，具有无序阴离子晶格的立方结构在室温下比四氢呋喃酮更稳定。像这样的结构关系在粗粒材料中是未知的。
Nanoparticles of ZrO 2 and HfO 2 with sizes around 5 nm are – depending on the production route - found in the cubic or tetragonal or monoclinc phase. To shed some light into this difference, an analysis of crystal structure, distances, and symmetry around the cations was performed on alumina coated nanoparticles prepared by the microwave plasma process. Within the range of accuracy, electron-diffraction and -microscopy revealed a possibly cubic cation lattice for both materials. In the case of ZrO 2 , the evaluation of the amplitude of the modified radial distribution function derived from extended x-ray absorption fine structure (EXAFS) data lead to a structure with a narrow distribution of oxygen ions in the first shell of neighbors. This is expected for the cubic structure. Comparing the imaginary part with model calculations, a distinct similarity with the cubic structure is obvious. In the second shell of neighbors, consisting of metal ions, one radial distribution peak is expected and found experimentally. Perturbed angular correlation measurements indicate a pronounced disorder of the positions of the first neighbors of the metal ions. Together with the EXAFS observation of a narrow radial distribution of the first neighbor oxygen ions, these measurements provide evidence for a randomc distribution of Zr-O bond angles in the vicinity of their crystallographic positions. Above 500°C a partially reversible transformation to almost perfect tetragonal symmetry is observed. Therefore, one has to conclude that the cubic structure with disordered anion lattice is more stable than the tetragonal one at room temperature. Structural relationships like this are unknown in coarse-grained material.