Table 4. Fractional Coordinates and Atomic Displacement Parameters for the Various Na3NiH5 Polymorphs Obtained from Rietveld Refinementa.
| atom | site | x | y | z | Uiso (Å2) |
|---|---|---|---|---|---|
| LP Na3NiH5 (Ambient, RT) | |||||
| Ni (Ni2+) | 4c | 0.8812(7) | 0.25 | 0.7557(14) | 0.0191(17) |
| Na1 (Na+) | 8d | 0.1528(12) | 0.0151(13) | 0.8209(18) | 0.025(3) |
| Na2 (Na+) | 4c | 0.0731(13) | 0.25 | 0.372(3) | 0.025(3) |
| LT-HP Na3NiH5 (∼5 GPa, 320 °C) | |||||
| Ni | 4c | 0 | 0.2427(15) | 0.25 | 0.017(2) |
| Na1 | 8e | 0.210(3) | 0 | 0 | 0.070(6) |
| Na2 | 4c | 0 | 0.691(4) | 0.25 | 0.070(6) |
| LT-HP Na3NiH5 (∼4.4 GPa, RT) | |||||
| Ni | 4c | 0 | 0.2391(16) | 0.25 | 0.013(3) |
| Na1 | 8e | 0.208(2) | 0 | 0 | 0.046(6) |
| Na2 | 4c | 0 | 0.675(3) | 0.25 | 0.046(6) |
| HT-HP Na3NiH5 (∼5 GPa, 365 °C) | |||||
| Ni | 4a | 0 | 0 | 0 | 0.0118(19) |
| Na1 | 8c | 0.25 | 0.25 | 0.25 | 0.054(3) |
| Na2 | 4b | 0.5 | 0.5 | 0.5 | 0.054(3) |
a
Hydrogen atoms for LP and LT-HP were introduced in the analysis from the DFT-optimized structures (Tables 1 and 2), and their positions were fixed during the refinement along with their ADPs [Uiso were set to 0.038 Å2 (Biso = 3 Å2)]. H atoms for HT-HP were placed at a site 48h with x = 0.15 (Ni–H = 1.521 Å) and an occupancy of 5/12. See Supporting Information for Rietveld refinement procedures and resulting plots (Figures S6 and S7).