Sarkar Abhishek, Loho Christoph, Velasco Leonardo, Thomas Tiju, Bhattacharya Subramshu S, Hahn Horst, Djenadic Ruzica
Institute of Nanotechnology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
Joint Research Laboratory Nanomaterials - Technische Universität Darmstadt and Karlsruhe Institute of Technology, Alarich-Weiss-Str. 2, 64287 Darmstadt, Germany.
Dalton Trans. 2017 Sep 28;46(36):12167-12176. doi: 10.1039/c7dt02077e. Epub 2017 Sep 4.
New multicomponent equiatomic rare earth oxides (ME-REOs) containing 3-7 rare earth elements (Ce, Gd, La, Nd, Pr, Sm and Y) in equiatomic proportions are synthesized using nebulized spray pyrolysis. All the systems crystallized as a phase pure fluorite type (Fm3[combining macron]m) structure in spite of the high chemical complexity. A nominal increase in the lattice parameter compared to CeO is observed in all ME-REOs. X-ray photoelectron spectroscopy performed on the ME-REOs confirmed that all the constituent rare earth elements are present in the 3+ oxidation state, except for Ce and Pr which are present in 4+ and in a mixed (3+/4+) oxidation state, respectively. The presence of Ce contributes substantially to the observed stability of the single phase structure. These new oxide systems have narrow direct band gaps in the range of 1.95-2.14 eV and indirect band gaps in the range of 1.40-1.64 eV, enabling light absorption over the entire visible spectral range. Furthermore, the oxygen vacancy concentration rapidly increases and then saturates with the number of rare earth elements that are incorporated into the ME-REOs. The lowering of the band gap is found to be closely related to the presence of multivalent Pr. Interestingly, the band gap values are relatively invariant with respect to the composition or thermal treatments. Considering the high level of oxygen vacancies present and the observed low band gap values, these new material systems can be of importance where the presence of oxygen vacancies is essential or in applications where a narrow band gap is desirable.
采用喷雾热解法合成了新的多组分等原子比稀土氧化物（ME-REOs），其中含有3 - 7种稀土元素（铈（Ce）、钆（Gd）、镧（La）、钕（Nd）、镨（Pr）、钐（Sm）和钇（Y）），且各元素原子比相等。尽管化学组成复杂，但所有体系均结晶为纯相萤石型（Fm3[combining macron]m）结构。在所有ME-REOs中，均观察到晶格参数相对于CeO有明显增加。对ME-REOs进行的X射线光电子能谱分析证实，除Ce以4 +氧化态、Pr以混合（3 +/4 +）氧化态存在外，所有组成稀土元素均以3 +氧化态存在。Ce的存在对所观察到的单相结构稳定性有很大贡献。这些新的氧化物体系具有1.95 - 2.14 eV范围内的窄直接带隙和1.40 - 1.64 eV范围内的间接带隙，能够在整个可见光谱范围内吸收光。此外，随着掺入ME-REOs中的稀土元素数量增加，氧空位浓度迅速增加然后饱和。发现带隙的降低与多价Pr的存在密切相关。有趣的是，带隙值相对于组成或热处理相对不变。考虑到存在的高氧空位水平和所观察到的低带隙值，这些新的材料体系在氧空位存在至关重要的情况下或在需要窄带隙的应用中可能具有重要意义。
