# High pressure study of sodium trihydride.
> 高圧下における三水素化ナトリウム（NaH₃）の構造と安定性に関する研究


## Abstract

Using diamond anvil cells combined with computational methods, the reaction between NaH and excess H₂ was examined at pressures reaching 78 GPa and temperatures near 2000 K. Powder X-ray diffraction revealed that sodium trihydride (NaH₃) forms above 27 GPa, adopting an orthorhombic crystal structure. Raman spectroscopy demonstrated the presence of quasi-molecular H₂ within the NaH lattice, with the H₂ stretching mode red-shifted by approximately 120 cm⁻¹ at 50 GPa relative to pure hydrogen. NaH₃ remained stable under room-temperature compression up to at least 78 GPa but decomposed below 18 GPa. Contrary to earlier experimental and theoretical predictions, no sodium polyhydrides beyond NaH₃ were produced when NaH was heated in excess H₂ between 27 and 75 GPa.

### Mechanism

Quasi-molecular H₂ is incorporated within the NaH lattice, stabilizing an orthorhombic NaH₃ phase under high pressure. Below 18 GPa the structure decomposes, and further hydrogenation to higher polyhydrides does not occur in the 27–75 GPa range.

## Bibliographic

- **Authors**: Marqueño T, Kuzovnikov MA, Osmond I, Dalladay-Simpson P, Hermann A, Howie RT, et al.
- **Journal**: Front Chem
- **Year**: 2023
- **PMID**: [38264124](https://pubmed.ncbi.nlm.nih.gov/38264124/)
- **DOI**: [10.3389/fchem.2023.1306495](https://doi.org/10.3389/fchem.2023.1306495)
- **PMC**: [PMC10803492](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10803492/)
- **Study type**: other
- **Delivery route**: not specified
- **Effect reported**: not assessed

## Delivery context

The delivery route is not clearly identifiable from this paper. For hydrogen intake, inhalation is the most efficient route; inhalation, however, carries explosion risk (empirical LFL of 10%; high-concentration devices are not recommended).

## Safety notes

The delivery route is not clearly identifiable from this paper. For hydrogen intake, inhalation is the most efficient route; inhalation, however, carries explosion risk (empirical LFL of 10%; high-concentration devices are not recommended).

See also:
- [Inhalation concentration and LFL / UFL](https://h2-papers.org/en/safety-notes/inhalation-concentration)
- [Consumer Affairs Agency accident cases](https://h2-papers.org/en/safety-notes/accident-cases)

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> **Cite as**: H2 Papers — PMID 38264124. https://h2-papers.org/en/papers/38264124
> **Source**: PubMed PMID [38264124](https://pubmed.ncbi.nlm.nih.gov/38264124/)