Boffelli M, Zhu W, Back M, Sponchia G, Francese T, Riello P, Benedetti A, Pezzotti G
Kyoto Institute of Technology and Research Institute for Nanoscience, Sakyo-ku, Matsugasaki, 606-8585 Kyoto, Japan.
J Phys Chem A. 2014 Oct 23;118(42):9828-36. doi: 10.1021/jp506923p. Epub 2014 Oct 10.
Systematic assessments of cathodoluminescence (CL) spectroscopy, Raman spectroscopy (RS), and X-ray diffraction (XRD) are presented for pure zirconia and for a series of Y-doped zirconia powders (henceforth, simply referred to as undoped ZrO2 and YSZ powders, respectively) synthesized according to a coprecipitation method of Zr and Y chlorides. Emphasis is placed here on spectral emissions related to oxygen-vacancy sites (i.e., oxygen hole states) equally detected from undoped and Y-doped ZrO2 samples, either as intrinsic defects or, extrinsically induced, by means of cathodoluminescence. Most counterintuitively, the undoped ZrO2 sample (i.e., the one with presumably the lowest amount of oxygen vacancies) experienced the strongest CL emission. A progressive "quenching" effect on CL emission with increasing the fraction of Y(3+) dopant could also be observed because the intrinsic vacancies present in the undoped lattice are the most efficient since they can trap two electrons to gain electrical neutrality. However, as soon as Y(3+) ions are introduced in the system, those intrinsic vacancies migrate to Y-sites in next-nearest-neighbor locations, namely in a less efficient lattice location. This phenomenon is tentatively referred to as "delocalization" of vacancy sites. Moreover, the fact that Y-doped zirconia series presents quite similar CL spectra compared to the undoped zirconia could be an evidence that the radiative centers of undoped and Y-doped ZrO2 are basically the same. A fitting procedure has been made aiming to give a rational description of the variation of the spectra morphology, and a parameter able to describe the monoclinic to tetragonal phase transformation has been found. This parameter and the overall set of CL data enabled us to quantitatively assess polymorphic phase fractions by CL spectroscopy in the scanning electron microscope.
本文介绍了对纯氧化锆以及通过共沉淀法合成的一系列钇掺杂氧化锆粉末（以下分别简称为未掺杂ZrO₂和YSZ粉末）进行的阴极发光光谱（CL）、拉曼光谱（RS）和X射线衍射（XRD）的系统评估。这里重点关注与氧空位相关的光谱发射（即氧空穴态），通过阴极发光，在未掺杂和钇掺杂的ZrO₂样品中均能检测到，这些氧空位无论是作为本征缺陷还是通过外部诱导产生。最违反直觉的是，未掺杂的ZrO₂样品（即氧空位含量可能最低的样品）经历了最强的CL发射。随着Y(3+)掺杂剂比例的增加，还可以观察到对CL发射的逐渐“猝灭”效应，因为未掺杂晶格中存在的本征空位是最有效的，因为它们可以捕获两个电子以获得电中性。然而，一旦Y(3+)离子引入系统，这些本征空位就会迁移到最近邻位置的Y位点，即在效率较低的晶格位置。这种现象被初步称为空位的“离域化”。此外，与未掺杂的氧化锆相比，钇掺杂氧化锆系列呈现出相当相似的CL光谱，这一事实可能证明未掺杂和钇掺杂的ZrO₂的辐射中心基本相同。已经进行了拟合程序，旨在对光谱形态的变化给出合理描述，并找到了一个能够描述单斜相到四方相转变的参数。该参数和CL数据的整体集使我们能够通过扫描电子显微镜中的CL光谱定量评估多晶型相分数。
