Interstitial-atom-induced phase transformation upon hydrogenation in vanadium
| Autor: | Eric H. Majzoub, Kenji Iwase, Akihiko Machida, Kouji Sakaki, Yumiko Nakamura, Hyunjeong Kim, Tetsu Watanuki |
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| Rok vydání: | 2018 |
| Předmět: |
Materials science
Hydrogen Hydride Mechanical Engineering Metals and Alloys Vanadium chemistry.chemical_element 02 engineering and technology Crystal structure 010402 general chemistry 021001 nanoscience & nanotechnology 01 natural sciences 0104 chemical sciences Crystallography Tetragonal crystal system Hydrogen storage chemistry Mechanics of Materials Phase (matter) Materials Chemistry Absorption (chemistry) 0210 nano-technology |
| Zdroj: | Journal of Alloys and Compounds. 750:33-41 |
| ISSN: | 0925-8388 |
| DOI: | 10.1016/j.jallcom.2018.03.345 |
| Popis: | The effect of interstitial atoms (nitrogen, carbon) on hydrogen storage properties in vanadium was investigated. When the N concentration was below 0.4 wt%, the plateau pressures increased with increasing N concentration during absorption and desorption and vanadium samples (body-centered cubic (BCC)) transformed to VH0.5 (body-centered tetragonal (BCT), c/a = 1.1) and then VH2 (face-centered cubic (FCC)). When the N concentration exceeded 0.6 wt%, a new single-phase region appeared in the pressure-composition isotherm, suggesting the formation of a new hydride phase. The X-ray diffraction data indicated that this new hydride phase was VH1.0 with a BCT structure and c/a = 1.24, and the phase transformation took place as V (BCC) became VH0.5 (BCT, c/a = 1.1), followed by VH1.0 (BCT, c/a = 1.24) and then VH2 (FCC). Density functional theory calculations indicated that the BCT structure model with hydrogen atoms fully occupying the octahedral sites (denoted as the Oz site) can explain the experimentally obtained crystal structure for VH1.0; they also indicated that the VH1.0 phase was stabilized by the addition of nitrogen. In addition, the N occupation site changed from the Oz site in VH0.5 and VH1.0 to the tetrahedral site (denoted as the T site) in VH2 in coordination with hydrogen during hydrogen absorption. A similar phenomenon was observed in carbon-containing vanadium. It can thus be concluded that the phase transformation pathway and stability of the hydride phases in the V–H system are highly sensitive to the addition of interstitial C and N atoms. |
| Databáze: | OpenAIRE |
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