High Pressure Phases of N-rich NxO Compoundsby Random Structure Search

• Main Authors: Hao-Chien Hung, 洪豪謙
• Other Authors: 王玉麟
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/q5394k

碩士 === 國立臺灣大學 === 物理學研究所 === 106 === We perform the random structure search for N2/O2 binary system under high pressure within the framework of density functional theory. We have found five types of structures to be energetically competitive under different circumstances. Including molecular, polymeric, sheet-like, slab-like and extended network structures. As N/O ratio increases up to 4 and pressure increases up to tens of GPa, our results show the tendency that the binary system prefers the last. The mechanism behind this phenomenon is that the systems in which all the nitrogen atoms are in three-fold coordination become energetically favorable under high pressure, since them can form extended network structures that have smaller volume. Intriguingly, for N4O system we found one novel molecular structure, named double pentagon (N8O2), which to our knowledge has not been reported before can be relatively stable within the pressure ranged from 61 to 85 GPa. Above 85 GPa the extended network structure becomes energetically favorable. The formation enthalpies and the details of each structure are presented and discussed.