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ε- MnO2 的结构是怎么样的啊？
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| ε- MnO2 的结构是怎么样的啊？请教各位，二氧化锰的主晶型有5种，他们的各个晶型的结构有什么不同？ |
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qfw_68
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sycjj(金币+10, 博学EPI+1):THS 2010-06-05 08:29:49
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ε-MnO2：六方软锰矿，英文： Akhtenskite 。 https://terms.nict.gov.tw/flyshe ... 218090256_77076.XLS ε-MnO2（Akhtenskite ）的晶体结构请见： https://www.handbookofmineralogy.org/pdfs/akhtenskite.pdf 二氧化锰具有多种晶形结构，如α-MnO2，β- MnO2，γ- MnO2，δ- MnO2，η- MnO2，ε－MnO2等。 α-MnO2也可称为隐钾锰矿，属四方晶系。其晶格参量为：a=9.82 Å，c=2.86 Å。每一个晶胞含有8个MnO2分子。其通式可暗示为：RxMn8O16·yH2O。其中，R代表Mn2 ,Ba2 ,K ,Li 等阳离子，x代表阳离子数，y代表结合水数，凡是大于6％。 β- MnO2一般不具有结合水，属四方晶系(金红石型)，其晶格常数为：a = 4.42Å, c = 2.87 Å。每一个晶胞含有2个二氧化锰分子。 γ- MnO2的通式可写为：MnO1.9～1.96(xH2O),其中x暗示约4％的化合水。实际上，在利用不同方法合成的样品中，结合水的含量略有不同，但一般在2％以上，这样才会使晶格不变。γ- MnO2属于斜层状复合材料 英文方晶系，其晶胞常数为:a = 4.52 Å, b = 9.27 Å, c = 2.86 Å.每一个晶胞含有4个二氧化锰分子。 另外，MnO2还具有δ，λ，ε等晶型结构，δ－MnO2为层状结构，在层间含有H2O和K 、Na 等阳离子。而λ－MnO2具有尖晶石结构。 https://www.biooin.com/information/viewnews-23381.htm 常见的MnO2具有α(四方)、β(四方)、γ(斜方)三种变体。软锰矿即β-MnO2。 https://www.crystalstar.org/Photo/ShowPhoto.asp?PhotoID=93 γ-MnO2是在天然Nsutite矿中发现的,后来多用化学法与电解法在一定条件下制备.不论是天然矿或是人工制备得到的,都不可能得到单晶的产品. https://d.wanfangdata.com.cn/Periodical_dc200501013.aspx λ-MnO2是典型的尖晶石结构，具有Fd3m空间对称群。氧呈立方密堆积，与锰形成[MnO6]八面体。在A[Mn2]O4的表示式中，氧离子占住八面体32c位置，锰离子占住八面体16d位置，A阳离子(如Li^+)占住四面体8a位置，其余四面体的晶格点则为空位。四面体晶格点(8a，48f)和八面体晶格点(16c)共面，形成相互连通的三维隧道结构 https://all.zcom.com/mag2/gongye ... 137/200503/5402724/ [ Last edited by qfw_68 on 2010-6-4 at 17:09 ] |
2楼2010-06-04 16:47:47
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sycjj(金币+10):XIEXIE 2010-06-05 08:34:19
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MnO2的多型很复杂，已经有非常全面的文献综述描述 主要区别在于1X1，1X2，2X2通道的组织方式不一样，还有微孪晶和de wolff无序的差别，要区别他们需要很好的XRD技术， 有一份130也的综述，如果有兴趣你可以读一下。 Chabre, Y. and J. Pannetier (1995). "Structural and Electrochemical Properties of the Proton Gamma-Mno2 System." Progress in Solid State Chemistry 23(1): 1-130. 摘要：This paper presents a structural description of the electrochemically active forms of manganese dioxide, known as gamma- and epsilon-MnO2 and used in Leclanche and alkaline batteries, in relation to an investigation of their electrochemical properties. These manganese dioxides, either natural (NMD) or prepared chemically (CMD) or electrochemically (EMD), have long been known to be an intergrowth of pyrolusite and ramsdellite units (a defect for which we coined the name of De Wolff disorder), but we show that another kind of structural defect, identified as microtwinning, is responsible for the poor quality of X-ray powder diffraction patterns of most gamma-MnO2 and for their difficult characterization. The model we introduce enables the reproduction of details of the diffraction patterns of these materials and, conversely, the quantitative determination of the structural disorder present. Comparison with experimental diffraction data shows that all synthetic samples of gamma-MD contain both microtwinning and De Wolff disorder. It is found that the amount of microtwinning is linked to the method of preparation of EMDs and that CMDs and EMDs exhibit different quantities of De Wolff disorder. With regard to the structure, a main conclusion of this work is that gamma- and epsilon-MnO2 are similar materials. Both forms derive from the ramsdellite structure, and differ only by the quantity of structural defects present, the so-called epsilon-MnO2 exhibiting more microtwinning than gamma-MnO2 samples. Practical methods to analyse X-ray powder diffraction patterns and calculate the amount of structural faults in real materials are proposed and lead to a new classification of gamma-MDs. It appears that only a small number of the possible members of the gamma-MnO2 structural family have been prepared up to now. The electrochemical behaviour of several MDs has been studied in alkaline electrolyte, using step potential electrochemical intercalation spectroscopy (SPECS) and in situ neutron powder diffraction. The successive steps of the first reduction of gamma-MDs, reduction of surface states, reduction of the ramsdellite units with proton intercalation and reduction of pyrolusite units, are analysed in detail. Correlations with the structural analysis of the pristine materials evidence the crucial role of disorder and defects in the electrochemical behaviour, and enables us to propose detailed mechanisms for the reduction of gamma-MnO2 up to one electron per Mn. A notable result is the fact that reduction proceeds along different paths according to how |
3楼2010-06-05 01:07:17
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