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ε- MnO2 的結構是怎么樣的�。�
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| ε- MnO2 的結構是怎么樣的�。空埥谈魑�，二氧化錳的主晶型有5種，他們的各個晶型的結構有什么不同？ |
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qfw_68
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sycjj(金幣+10, 博學EPI+1):THS 2010-06-05 08:29:49
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ε-MnO2：六方軟錳礦，英文： Akhtenskite 。 https://terms.nict.gov.tw/flyshe ... 218090256_77076.XLS ε-MnO2（Akhtenskite ）的晶體結構請見： https://www.handbookofmineralogy.org/pdfs/akhtenskite.pdf 二氧化錳具有多種晶形結構，如α-MnO2，β- MnO2，γ- MnO2，δ- MnO2，η- MnO2，ε－MnO2等。 α-MnO2也可稱為隱鉀錳礦，屬四方晶系。其晶格參量為：a=9.82 Å，c=2.86 Å。每一個晶胞含有8個MnO2分子。其通式可暗示為：RxMn8O16·yH2O。其中，R代表Mn2 ,Ba2 ,K ,Li 等陽離子，x代表陽離子數(shù)，y代表結合水數(shù)，凡是大于6％。 β- MnO2一般不具有結合水，屬四方晶系(金紅石型)，其晶格常數(shù)為：a = 4.42Å, c = 2.87 Å。每一個晶胞含有2個二氧化錳分子。 γ- MnO2的通式可寫為：MnO1.9～1.96(xH2O),其中x暗示約4％的化合水。實際上，在利用不同方法合成的樣品中，結合水的含量略有不同，但一般在2％以上，這樣才會使晶格不變。γ- MnO2屬于斜層狀復合材料 英文方晶系，其晶胞常數(shù)為:a = 4.52 Å, b = 9.27 Å, c = 2.86 Å.每一個晶胞含有4個二氧化錳分子。 另外，MnO2還具有δ，λ，ε等晶型結構，δ－MnO2為層狀結構，在層間含有H2O和K 、Na 等陽離子。而λ－MnO2具有尖晶石結構。 https://www.biooin.com/information/viewnews-23381.htm 常見的MnO2具有α(四方)、β(四方)、γ(斜方)三種變體。軟錳礦即β-MnO2。 https://www.crystalstar.org/Photo/ShowPhoto.asp?PhotoID=93 γ-MnO2是在天然Nsutite礦中發(fā)現(xiàn)的,后來多用化學法與電解法在一定條件下制備.不論是天然礦或是人工制備得到的,都不可能得到單晶的產(chǎn)品. https://d.wanfangdata.com.cn/Periodical_dc200501013.aspx λ-MnO2是典型的尖晶石結構，具有Fd3m空間對稱群。氧呈立方密堆積，與錳形成[MnO6]八面體。在A[Mn2]O4的表示式中，氧離子占住八面體32c位置，錳離子占住八面體16d位置，A陽離子(如Li^+)占住四面體8a位置，其余四面體的晶格點則為空位。四面體晶格點(8a，48f)和八面體晶格點(16c)共面，形成相互連通的三維隧道結構 https://all.zcom.com/mag2/gongye ... 137/200503/5402724/ [ Last edited by qfw_68 on 2010-6-4 at 17:09 ] |
2樓2010-06-04 16:47:47
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sycjj(金幣+10):XIEXIE 2010-06-05 08:34:19
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MnO2的多型很復雜，已經(jīng)有非常全面的文獻綜述描述 主要區(qū)別在于1X1，1X2，2X2通道的組織方式不一樣，還有微孿晶和de wolff無序的差別，要區(qū)別他們需要很好的XRD技術， 有一份130也的綜述，如果有興趣你可以讀一下。 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樓2010-06-05 01:07:17
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4樓2012-02-23 17:18:12
5樓2012-06-14 18:22:05
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