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Atomic scale dynamics of a solid state chemical reaction directly determined by annular dark-field electron microscopy.

Pennycook TJ, Jones L, Pettersson H, Coelho J, Canavan M, Mendoza-Sanchez B, Nicolosi V, Nellist PD - Sci Rep (2014)

Bottom Line: Here we combine these benefits to record the motions and quantitative changes in the occupancy of individual atomic columns during a solid-state chemical reaction in manganese oxides.These oxides are of great interest for energy-storage applications such as for electrode materials in pseudocapacitors.The results demonstrate we now have the experimental capability to understand the complex atomic mechanisms involved in phase changes and solid state chemical reactions.

View Article: PubMed Central - PubMed

Affiliation: 1] SuperSTEM Laboratory, STFC Daresbury, Keckwick Lane, Warrington WA4 4AD, United Kingdom [2] Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom.

ABSTRACT
Dynamic processes, such as solid-state chemical reactions and phase changes, are ubiquitous in materials science, and developing a capability to observe the mechanisms of such processes on the atomic scale can offer new insights across a wide range of materials systems. Aberration correction in scanning transmission electron microscopy (STEM) has enabled atomic resolution imaging at significantly reduced beam energies and electron doses. It has also made possible the quantitative determination of the composition and occupancy of atomic columns using the atomic number (Z)-contrast annular dark-field (ADF) imaging available in STEM. Here we combine these benefits to record the motions and quantitative changes in the occupancy of individual atomic columns during a solid-state chemical reaction in manganese oxides. These oxides are of great interest for energy-storage applications such as for electrode materials in pseudocapacitors. We employ rapid scanning in STEM to both drive and directly observe the atomic scale dynamics behind the transformation of Mn3O4 into MnO. The results demonstrate we now have the experimental capability to understand the complex atomic mechanisms involved in phase changes and solid state chemical reactions.

No MeSH data available.


Related in: MedlinePlus

Model of the phase front advance.(a), The first plane of Mn3O4 is indicated by the black arrow. This plane contains Mn atoms in positions shared by MnO, but the columns contain half as many Mn atoms as in MnO. (b), To advance the phase front forwards, these vacancies must be filled. To convert the next row of columns then requires the pairs of tetrahedral Mn atoms to move into a single column as in (c). (d), Continuing the conversion is then just a repeat of these two steps. Mn and O atoms are shown in purple and red respectively.
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f2: Model of the phase front advance.(a), The first plane of Mn3O4 is indicated by the black arrow. This plane contains Mn atoms in positions shared by MnO, but the columns contain half as many Mn atoms as in MnO. (b), To advance the phase front forwards, these vacancies must be filled. To convert the next row of columns then requires the pairs of tetrahedral Mn atoms to move into a single column as in (c). (d), Continuing the conversion is then just a repeat of these two steps. Mn and O atoms are shown in purple and red respectively.

Mentions: Figure 2 displays a model of the phase front advance based on the dynamic STEM observations. In figure 2a the structure of the first plane of the spinel Mn3O4 at the phase front only differs significantly from MnO in that its B type Mn columns have half the occupation as the A type column in the MnO. The Mn atoms that are there already occupy positions that should be occupied in MnO. As soon as the vacant sites are filled, the phase front advances. Aside from slight changes in bond lengths, the oxygen atoms do not need to rearrange significantly. This is just what we see with dynamic STEM. The B type columns simply increase in intensity until they reach the intensity of A type columns, indicating that enough additional Mn atoms have diffused into the column to fill the vacant sites. This advances the phase front a single plane. From the ADF imaging we see the C type Mn columns merge into a single column with twice the occupation. Figure 2b–c show how this occurs, advancing the phase front forward another plane. The C type columns contain tetrahedrally coordinated Mn atoms. Each C type column contains Mn atoms spaced midway between those of the adjacent C type column in the [100] direction. All that is needed to convert each pair of C type columns into a single octahedrally coordinated A type column is for them to merge by aligning at their midpoint. As with the previous plane, the oxygen atoms do not need to rearrange significantly. These two basic steps then repeat to continue the advance of the phase front.


Atomic scale dynamics of a solid state chemical reaction directly determined by annular dark-field electron microscopy.

Pennycook TJ, Jones L, Pettersson H, Coelho J, Canavan M, Mendoza-Sanchez B, Nicolosi V, Nellist PD - Sci Rep (2014)

Model of the phase front advance.(a), The first plane of Mn3O4 is indicated by the black arrow. This plane contains Mn atoms in positions shared by MnO, but the columns contain half as many Mn atoms as in MnO. (b), To advance the phase front forwards, these vacancies must be filled. To convert the next row of columns then requires the pairs of tetrahedral Mn atoms to move into a single column as in (c). (d), Continuing the conversion is then just a repeat of these two steps. Mn and O atoms are shown in purple and red respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4273600&req=5

f2: Model of the phase front advance.(a), The first plane of Mn3O4 is indicated by the black arrow. This plane contains Mn atoms in positions shared by MnO, but the columns contain half as many Mn atoms as in MnO. (b), To advance the phase front forwards, these vacancies must be filled. To convert the next row of columns then requires the pairs of tetrahedral Mn atoms to move into a single column as in (c). (d), Continuing the conversion is then just a repeat of these two steps. Mn and O atoms are shown in purple and red respectively.
Mentions: Figure 2 displays a model of the phase front advance based on the dynamic STEM observations. In figure 2a the structure of the first plane of the spinel Mn3O4 at the phase front only differs significantly from MnO in that its B type Mn columns have half the occupation as the A type column in the MnO. The Mn atoms that are there already occupy positions that should be occupied in MnO. As soon as the vacant sites are filled, the phase front advances. Aside from slight changes in bond lengths, the oxygen atoms do not need to rearrange significantly. This is just what we see with dynamic STEM. The B type columns simply increase in intensity until they reach the intensity of A type columns, indicating that enough additional Mn atoms have diffused into the column to fill the vacant sites. This advances the phase front a single plane. From the ADF imaging we see the C type Mn columns merge into a single column with twice the occupation. Figure 2b–c show how this occurs, advancing the phase front forward another plane. The C type columns contain tetrahedrally coordinated Mn atoms. Each C type column contains Mn atoms spaced midway between those of the adjacent C type column in the [100] direction. All that is needed to convert each pair of C type columns into a single octahedrally coordinated A type column is for them to merge by aligning at their midpoint. As with the previous plane, the oxygen atoms do not need to rearrange significantly. These two basic steps then repeat to continue the advance of the phase front.

Bottom Line: Here we combine these benefits to record the motions and quantitative changes in the occupancy of individual atomic columns during a solid-state chemical reaction in manganese oxides.These oxides are of great interest for energy-storage applications such as for electrode materials in pseudocapacitors.The results demonstrate we now have the experimental capability to understand the complex atomic mechanisms involved in phase changes and solid state chemical reactions.

View Article: PubMed Central - PubMed

Affiliation: 1] SuperSTEM Laboratory, STFC Daresbury, Keckwick Lane, Warrington WA4 4AD, United Kingdom [2] Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, United Kingdom.

ABSTRACT
Dynamic processes, such as solid-state chemical reactions and phase changes, are ubiquitous in materials science, and developing a capability to observe the mechanisms of such processes on the atomic scale can offer new insights across a wide range of materials systems. Aberration correction in scanning transmission electron microscopy (STEM) has enabled atomic resolution imaging at significantly reduced beam energies and electron doses. It has also made possible the quantitative determination of the composition and occupancy of atomic columns using the atomic number (Z)-contrast annular dark-field (ADF) imaging available in STEM. Here we combine these benefits to record the motions and quantitative changes in the occupancy of individual atomic columns during a solid-state chemical reaction in manganese oxides. These oxides are of great interest for energy-storage applications such as for electrode materials in pseudocapacitors. We employ rapid scanning in STEM to both drive and directly observe the atomic scale dynamics behind the transformation of Mn3O4 into MnO. The results demonstrate we now have the experimental capability to understand the complex atomic mechanisms involved in phase changes and solid state chemical reactions.

No MeSH data available.


Related in: MedlinePlus