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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >In situ powder X-ray diffraction study of the hydro-thermal formation of LiMn_2O_4 nanocrystallites
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In situ powder X-ray diffraction study of the hydro-thermal formation of LiMn_2O_4 nanocrystallites

机译：LiMn_2O_4纳米微晶水热形成的原位粉末X射线衍射研究

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In situ measurements of the hydrothermal formation of LiMn_2O_4 (LMO) nanocrystallites reveal that the reaction progresses in steps, each creating a different crystalline phase. The reaction route is summarized as KMnO_4→disordered δ-MnO_2→(ordered δ-MnO_2)→LiMn_2O_4→(γ-Mn_2O_3)→Mn_3O_4. The phase purity of LMO can be controlled by reaction time and temperature where phase pure LMO is obtained after 150-210 seconds at 220 ℃ or 45-140 seconds at 260 ℃. It is also concluded that production of phase pure LMO by this method comes at the price of reduced reaction yield. From the observed reaction route an alternative way to control the phase purity is proposed by changing the amount of reducing agent. This hypothesis is rejected by a set of in situ measurements showing that the reaction kinetics of subsequent reaction steps hinders the formation of phase pure LMO. From the observation of unit cell changes as function of the transformation from LMO to Mn_3O_4 three distinct reaction parts are observed. This indicates that the reaction is a solid-solid reaction with a phase boundary. The in situ measurements reveal that LMO first appears in the reaction solution as thin platelets with sizes ranging from 3-13 nm. As the reaction progresses the crystallites grow faster along the [111] direction giving rod-like shaped crystallites in the end. The LMO crystallites start off with the same shape at all temperatures investigated indicating that they form from δ-MnO_2 crystallites.
机译：LiMn_2O_4（LMO）纳米晶体的水热形成的原位测量表明，反应是逐步进行的，每个过程都会产生不同的结晶相。反应路线概括为KMnO_4→无序的δ-MnO_2→（有序的δ-MnO_2）→LiMn_2O_4→（γ-Mn_2O_3）→Mn_3O_4。 LMO的相纯度可通过反应时间和温度控制，在220℃下150-210秒或260℃下45-140秒后可获得纯LMO相。还得出结论，用这种方法生产相纯的改性活生物体是以降低反应产率为代价的。根据观察到的反应路线，提出了通过改变还原剂的量来控制相纯度的另一种方法。该假设被一组原位测量所拒绝，该组原位测量表明后续反应步骤的反应动力学阻碍了相纯LMO的形成。从观察到的晶胞变化作为从LMO到Mn_3O_4的转变的函数，观察到三个不同的反应部分。这表明该反应是具有相界的固-固反应。原位测量表明，LMO首先以3-13 nm大小的薄片形式出现在反应溶液中。随着反应的进行，微晶沿[111]方向生长更快，最终形成棒状微晶。在所有研究的温度下，LMO晶体均以相同的形状开始，这表明它们是由δ-MnO_2晶体形成的。

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