Yttrium Manganese Oxide Phase Stability and Selectivity Using Lithium Carbonate Assisted Metathesis Reactions
Yttrium Manganese Oxide Phase Stability and Selectivity Using Lithium Carbonate Assisted Metathesis Reactions
复制标题
使用碳酸锂辅助复分解反应测定钇锰氧化物相稳定性和选择性
DOI：
10.1021/acs.inorgchem.9b02075
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发表时间：
2019
影响因子：
4.6
通讯作者：
Neilson, James R.
中科院分区：
文献类型：
--
作者：
Todd, Paul K.;Smith, Antoinette M.;Neilson, James R.
在固态化学中，如果稳定相的合成不切实际，例如在相对较低的温度下发生分解或多晶型转变，则通常会错过稳定相。在复合氧化物的制备中，反应温度通常超过1000 °C，反应途径几乎没有控制。因此，探索合成复合氧化物的先决条件是确定在低温下具有动力学能力的中间体的反应，如辅助复分解反应所提供的。本文用同步辐射X射线衍射法研究了Mn_2O_3 + 2.2YCl_3·6H_2O +3Li_2CO_3 → 2YMnO_3 + 5.8LiCl +0.2LiYCl_4 + 3CO_2的辅助复分解反应。通过改变气氛、氧气和惰性气体，在850 °C下，反应产物由过氧化的钙钛矿型YMnO 3 +δ转变为六方晶系YMnO 3。通过对反应途径的分析，揭示了形成YMnO_3相的两条平行反应途径：（1）金属氧化物在LiCl助熔剂中的缓慢反应（Y_2 O_3 + Mn_2 O_32 YMnO_3）和（2）三元中间体的快速反应（YOCl + LiMnO_2 → LiCl + YMnO_3）。对照反应表明，两种提出的途径在隔离导致产物的形成，但三元中间体（YOCl + LiMnO 2 → LiCl + YMnO 3）的直接制备发生在较低的温度（500 °C）和较短的时间（<24 h），并形成名义上的化学计量的正交YMnO 3。这些三元中间体的反应速率比氯化钇缓慢逐步氧化为Y2 O3（YCl 3 → YOCl → Y3 O 4Cl → Y2 O3）的反应速率更快，而Y2 O3相对惰性。这些结果支持一个动力学控制的反应途径，以形成YMnO 3相辅助复分解反应，通过改变反应气氛实现相选择性。
In solid-state chemistry, stable phases are often missed if their synthesis is impractical, such as when decomposition or a polymorphic transition occurs at relatively low temperature. In the preparation of complex oxides, reaction temperatures commonly exceed 1000 °C with little to no control of the reaction pathway. Thus, a prerequisite for exploring the synthesis of complex oxides is to identify reactions with intermediates that are kinetically competent at low temperatures, as provided by assisted metathesis reactions. Here, we study the assisted metathesis reaction Mn2O3+ 2.2YCl3·6H2O + 3Li2CO3→ 2YMnO3+ 5.8LiCl + 0.2LiYCl4+ 3CO2usingin situsynchrotron X-ray diffraction. By changing the atmosphere, oxygen vs inert gas, the reaction product changes from the overoxidized perovskite YMnO3+δto the hexagonal YMnO3polymorph at the reaction temperature of 850 °C, respectively. Analysis of the reaction pathways reveals two parallel reaction pathways in forming YMnO3phases: (1) the slow reaction of metal oxides in a LiCl flux (Y2O3+ Mn2O32YMnO3) and (2) the fast reaction from ternary intermediates (YOCl + LiMnO2→ LiCl + YMnO3). Control reactions reveal that both proposed pathways in isolation result in product formation, but the direct preparation of ternary intermediates (YOCl + LiMnO2→ LiCl + YMnO3) occurs at lower temperatures (500 °C) and shorter times (<24 h) and forms nominally stoichiometric orthorhombic YMnO3. These ternary intermediates react at a faster rate than the slow stepwise oxygenation of yttrium chloride to Y2O3(YCl3→ YOCl → Y3O4Cl → Y2O3), which is relatively inert. These results support a kinetically controlled reaction pathway to form YMnO3phases in assisted metathesis reactions with phase selectivity achievable through changes to reaction atmosphere.