Phase Diagram Analysis of High-Pressure/High-Temperature Polymorphs of Ammonia Borane.
Inorg Chem
; 63(7): 3283-3291, 2024 Feb 19.
Article
in En
| MEDLINE
| ID: mdl-38315663
ABSTRACT
Ammonia borane (NH3BH3) is a promising hydrogen-storage material because of its high hydrogen density. It is employed as a hydrogen source when synthesizing superconducting polyhydrides under high pressure. Additionally, NH3BH3 is a crystallographically interesting compound that features protonic hydrogen (Hδ+) and hydridic hydrogen (Hδ-), and it forms a dihydrogen bond, which explains its stable existence as a solid. Herein, X-ray diffraction experiments were performed at high pressures (HPs) and high temperatures (HTs) of up to 30 GPa and 300 °C, respectively, to investigate the HP/HT phase diagram of NH3BH3. A new HP/HT phase (HPHT2) was identified above 9 GPa and 150 °C. Crystal-structure analysis using the Rietveld method and stability verification using density functional theory calculations revealed that HPHT2 has a P21/n (Z = 4) structure, similar to that of a previously reported HP/HT phase (HPHT) that appears at a lower pressure. HPHT2 is denser than the HP phases that appear at room temperature (HP1 and HP2) at the same pressure (up to â¼17 GPa). In the phase diagram, the phase-boundary line between HPHT and HP1 is a downward convex curve. These unconventional phenomena in the density and phase boundary can be attributed to the influence of dihydrogen bonding on the crystal structure and phase diagram.
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01-internacional
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MEDLINE
Language:
En
Journal:
Inorg Chem
/
Inorg. chem
/
Inorganic chemistry
Year:
2024
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Article
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