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Structural and Dynamic Properties of the High-Pressure, High-Temperature Phase of Solid Ammonia Borane
- Wang, Liancheng, Duan, Defang, Zhao, Bin, Bao, Kuo, Yu, Hongyu
- Journal of physical chemistry 2019 v.123 no.11 pp. 6326-6332
- X-ray diffraction, ammonia, hydrogen, molecular dynamics, phase transition, simulation models, temperature
- The increasing decomposition temperature of solid ammonia borane under high pressure introduces a solid–solid phase transition preceding decomposition. An earlier X-ray diffraction experiment suggested the newfound high-pressure, high-temperature phase has a Pnma space group symmetry with four molecules in the unit cell. However, ab initio molecular dynamics simulations indicated that this structure was unstable and transformed into a new structure with same space symmetry but different dihydrogen-bonding network. Moreover, the Pnma phase is a proton-ordered phase, and the hydrogen continuously rotates around the molecular axis. The role of dihydrogen bonds in the phase structure and phase transition was also discussed.