NMR Study of Anion Dynamics in Solid KAlH4
| Autor: | Eric G. Sorte, Zayd L. Ma, Robert C. Bowman, Samuel B. Emery, Sophia E. Hayes, Mark S. Conradi, Tim Ellis-Caleo, Eric H. Majzoub, Blake A. Hammann |
|---|---|
| Rok vydání: | 2014 |
| Předmět: |
Materials science
Hydrogen Diffusion media_common.quotation_subject Dynamics (mechanics) chemistry.chemical_element Activation energy Asymmetry Molecular physics Surfaces Coatings and Films Electronic Optical and Magnetic Materials Ion General Energy chemistry Electric field Quadrupole Physical and Theoretical Chemistry media_common |
| Zdroj: | The Journal of Physical Chemistry C. 118:5725-5732 |
| ISSN: | 1932-7455 1932-7447 |
| DOI: | 10.1021/jp5001978 |
| Popis: | 1H and 27Al NMR is used to reveal the motions of AlH4 anions in KAlH4. Line-narrowing from rotations and from translational diffusion is observed in the NMR of both nuclei. Unlike the anions in NaAlH4 and LiAlH4 that are not rotating on the NMR time scale at room temperature, the KAlH4 anions are already rotating rapidly at 23 °C. Based on the onset of rotation-induced line narrowing, the 1H T1 minimum, and the low- temperature hydrogen T1ρ minimum associated with reorientations, the rotational activation energy Erot,act = 0.28 eV is determined. Similarly, we use the onset temperature of translational motion-induced line narrowing and the high-temperature T1ρ minimum to determine the diffusion activation energy Ediff,act = 0.70 eV. Lack of sharp structure in the first-order quadrupole pattern and the absence of second-order quadrupole structure in the 27Al NMR data suggest asymmetry (η ≠ 0) and/or variations in the anion electric field gradients from structural disorder. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|