Reduced GeO2 Nanoparticles: Electronic Structure of a Nominal GeOx Complex and Its Stability under H2 Annealing.
Reduced GeO2 Nanoparticles: Electronic Structure of a Nominal GeOx Complex and Its Stability under H2 Annealing.
复制标题
还原的 GeO2 纳米粒子：标称 GeOx 配合物的电子结构及其在 H2 退火下的稳定性
DOI：
10.1038/srep17779
复制
发表时间：
2015-12-04
影响因子：
4.6
通讯作者：
Liu L
中科院分区：
文献类型：
--
作者：
Zhao J;Yang L;McLeod JA;Liu L
名义上的GeOx（x≤2）化合物包含Ge、低价锗氧化物和GeO₂的混合物，但具体成分和结晶度可能因材料而异。在本研究中，我们通过化学还原GeO₂合成了GeOx纳米颗粒，并对新制备的样品和暴露在环境条件下的样品进行了比较研究。尽管这两种化合物名义上都是GeOx，但它们表现出不同的X射线衍射图案。利用X射线吸收精细结构（XAFS）分析GeOx的详细结构。我们发现这两种初始的GeOx化合物具有完全不同的成分：新制备的GeOx包含由GeOx连接的大的无定形Ge簇，而在暴露于空气后，Ge簇被GeO₂ - GeOx复合物所取代。此外，这两种GeOx产物在H₂退火下经历不同的结构重排，在最终转变为金属Ge之前产生不同的中间相。在新制备的GeOx中，无定形Ge保持稳定，GeOx逐渐被还原为Ge，导致最终形成由GeOx连接的结晶Ge晶粒结构。另一方面，暴露于空气的GeOx经历GeO₂→GeOx→Ge的转变，其中H₂在中间阶段诱导产生氧空位。在高温下氧化物被完全去除。
A nominal GeOx (x ≤ 2) compound contains mixtures of Ge, Ge suboxides, and GeO2, but the detailed composition and crystallinity could vary from material to material. In this study, we synthesize GeOx nanoparticles by chemical reduction of GeO2, and comparatively investigate the freshly prepared sample and the sample exposed to ambient conditions. Although both compounds are nominally GeOx, they exhibit different X-ray diffraction patterns. X-ray absorption fine structure (XAFS) is utilized to analyse the detailed structure of GeOx. We find that the two initial GeOx compounds have entirely different compositions: the fresh GeOx contains large amorphous Ge clusters connected by GeOx, while after air exposure; the Ge clusters are replaced by a GeO2-GeOx composite. In addition, the two GeOx products undergo different structural rearrangement under H2 annealing, producing different intermediate phases before ultimately turning into metallic Ge. In the fresh GeOx, the amorphous Ge remains stable, with the GeOx being gradually reduced to Ge, leading to a final structure of crystalline Ge grains connected by GeOx. The air-exposed GeOx on the other hand, undergoes a GeO2→GeOx→Ge transition, in which H2 induces the creation of oxygen vacancies at intermediate stage. A complete removal of oxides occurs at high temperature.