Confalonieri Giorgia, Rotiroti Nicola, Bernasconi Andrea, Dapiaggi Monica
Dipartimento di Scienze della Terra, Università degli Studi di Milano, 20133 Milano, Italy.
Dipartimento di Scienze Chimiche e Geologiche, Università degli Studi di Modena e Reggio Emilia, 41125 Modena, Italy.
Nanomaterials (Basel). 2020 Apr 26;10(5):824. doi: 10.3390/nano10050824.
Spinel gahnite (ZnAlO) has been obtained through a hydrothermal synthesis method with a grain size of about 2 nm. The sample was calcined for a few hours at two different temperatures (800 and 900 °C) in order to obtain larger grain sizes to be analyzed by means of powder diffraction with the Rietveld method, and by means of total scattering with the Pair Distribution Function (PDF) method. The idea is to compare the average to the local structure, as a function of increasing grain size. The total scattering data were collected at the European Synchrotron Radiation Facility (ESRF), Grenoble. The samples have been also characterised by means of high resolution Transmission Electron Microscopy (TEM), showing an increasing grain size up to about 9 nm. The average structure presented variations in the inversion degree and an increase in grain size. TEM observations demonstrated that the small crystals are well crystallised: the high resolution images neatly showed the atomic planes, even in the smallest particles. However, the average structure did not properly fit the PDF data in the local region, owing to a slightly different coordination among the octahedra. A new structural model is proposed for the local region of the PDF, that helped our understanding of the differences between a real nanostructured sample and that of a microcrystalline one. The oxygen disorder, due to the inversion grade of the spinel, is demonstrates to be at the basis of the local deviation. No signals of interstitial Zn atoms were detected.
通过水热合成法制备出了晶粒尺寸约为2纳米的尖晶石锌铝尖晶石（ZnAlO）。为了获得更大的晶粒尺寸以便用Rietveld方法进行粉末衍射分析以及用对分布函数（PDF）方法进行全散射分析，将样品在800和900℃这两个不同温度下煅烧了几个小时。目的是比较平均结构与局部结构随晶粒尺寸增大的变化情况。全散射数据是在法国格勒诺布尔的欧洲同步辐射装置（ESRF）收集的。样品还通过高分辨率透射电子显微镜（TEM）进行了表征，结果显示晶粒尺寸增大到了约9纳米。平均结构在反演程度上出现了变化，且晶粒尺寸有所增加。TEM观察表明小晶体结晶良好：即使是最小的颗粒，高分辨率图像也清晰地显示出了原子平面。然而，由于八面体之间的配位略有不同，平均结构在局部区域与PDF数据拟合得并不理想。针对PDF的局部区域提出了一种新的结构模型，这有助于我们理解真实纳米结构样品与微晶样品之间的差异。结果表明，由于尖晶石的反演程度导致的氧无序是局部偏差的根源。未检测到间隙锌原子的信号。
