| Résumé | The pressure-dependent structural and vibrational properties of barium hydride have been studied up to 22 GPa at room temperature by means of powder x-ray diffraction, Raman spectroscopy, and first-principles calculations. At ambient conditions, BaH2 crystallizes in the cotunnite structure (Pnma). A reversible, first-order structural phase transition is observed at 1.6 GPa. The high-pressure phase can be indexed by a hexagonal unit cell with a proposed Ni2In structure (P63/mmc), with the Ba and H atoms in special positions. The experimental volume compression of the high-pressure phase yields an isothermal bulk modulus B0=24(1) GPa (B<sub>0</sub><sup>[prime]</sup> fixed at 4.13). This compares favorably with the results of the first-principles calculations, which reproduce the first-order nature of the transition. The relevance of these results is discussed in the contexts of metal hydrides in particular and ionic AX2 (A=metal) compounds in general. |
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