Gespeichert in:
| Hauptverfasser: | , , , , , |
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| Format: | Preprint |
| Veröffentlicht: |
2025
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| Schlagworte: | |
| Online-Zugang: | https://arxiv.org/abs/2508.03874 |
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Inhaltsangabe:
- Hexammine magnesium borohydride, Mg(NH$_3$)$_6$(BH$_4$)$_2$, consists of adducted NH$_3$ molecules locked in a matrix of Mg cations and borohydride anions. It is a candidate material for hydrogen storage, with 16.8wt\% hydrogen stored in both the NH$_3$ and borohydride anions. It also may be of interest as a Mg$^{2+}$ conducting electrolyte in solid state batteries. Its crystal structure has, until now, eluded a proper structural solution due to ambiguity regarding the NH$_3$ position and behaviour. In this work, we show using synchrotron X-ray diffraction that the room-temperature structure can be solved only with a model assuming orientational disorder of ammonia molecules within the crystal structure. Cooling the sample to 120\,K yields additional Bragg peaks, which can only be solved with a unit cell expansion consistent with a freezing of the orientational freedom of ammonia molecules. Using this insight from the structure solution, we perform a full assignment of the vibrational modes in the room-temperature IR spectrum.