- Title
- Kinetics of the thermally-induced structural rearrangement of γ-MnO₂
- Creator
- Dose, Wesley M.; Sharma, Neeraj; Webster, Nathan A. S.; Peterson, Vanessa K.; Donne, Scott W.
- Relation
- Journal of Physical Chemistry Part C Vol. 118, Issue 42, p. 24257-24265
- Publisher Link
- http://dx.doi.org/10.1021/jp506914j
- Publisher
- American Chemical Society (ACS)
- Resource Type
- journal article
- Date
- 2014
- Description
- This work presents a temperature-dependent and time-resolved X-ray and neutron diffraction study of the thermally induced structural rearrangement of γ-MnO₂. Here, we study electrochemically prepared γ-MnO₂, the manganese dioxide phase used in the majority of battery applications, which we find to be ~64% ramsdellite [a = 4.4351(6) Å, b = 9.486(2) Å, c = 2.8128(7) Å, and V = 118.33(3) ų] and ~36% pyrolusite [a = 4.718(3) Å, c = 2.795(2) Å, and V = 62.22(8) Å3]. Taking a deeper look at the kinetics of the structural rearrangement, we find two steps: a fast transition occurring within 4-8 min with a temperature-dependent ramsdellite to pyrolusite transformation (rate constant 0.11-0.74 min⁻¹) and a slow transition over 4h that densifies (with changes in unit cell and volume) the ramsdellite and pyrolusite phases to give structures that appear to be temperature-independent. This effectively shows that γ/β-MnO₂ prepared in the range of 200-400°C consists of temperature-independent structures of ramsdellite, unit cell a = 4.391(1) Å, b = 9.16(5) Å, c = 2.847(1) Å, and V = 114.5(6) ų, and pyrolusite, unit cell a = 4.410(2) Å, c = 2.869(2) Å, and V = 55.79(4) ų, with a temperature-dependent pyrolusite fraction between 0.45 and 0.77 and increasing with temperature. Therefore, we have linked the temperature and time of heat treatment to the structural evolution of γ-MnO₂, which will aid the optimization of γ/β-MnO₂ as used in Li-primary batteries.
- Subject
- γ -MnO₂; thermally-induced structural rearrangement; ramsdellite; pyrolusite; temperature-dependent
- Identifier
- http://hdl.handle.net/1959.13/1297278
- Identifier
- uon:19411
- Identifier
- ISSN:1932-7447
- Language
- eng
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