Thermodynamic stability of elemental boron allotropes with varying numbers of interstitial atoms
- National Institute for Materials Science (NIMS), Tsukuba (Japan)
- Tokyo Univ. of Science (Japan)
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
- Univ. of Tokyo, Chiba (Japan)
Elemental boron exists in multiple allotropes, each characterized by structures containing icosahedral subunits. These structures have interstitial sites between the icosahedral subunits that are partially occupied. The number of atoms in the unit cell varies depending on the occupancy of these interstitial sites. Here we have investigated the thermodynamic stability of boron allotropes for different numbers of atoms in the unit cell by calculating the free energies, including the contribution of phonons. It has been found that β-rhombohedral boron is most stable with 107 atoms/cell at low temperatures, while it becomes most stable with 105 atoms/cell above 1700 K. This suggests the occurrence of a phase transition at this temperature, which could account for the large variation in the number of atoms in the unit cell for β-rhombohedral boron samples. α-tetragonal boron is consistently most stable with 52 atom/cell and becomes unstable with more than 52 atoms/cell. Similar to β-rhombohedral boron, β-tetragonal boron may undergo a phase transition between 192 and 190 atoms/cell configurations. However, the thermodynamic stability of pure β-tetragonal boron has been questioned in comparison with other allotropes.
- Research Organization:
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division (MSE); Japan Society for the Promotion of Science (JSPS) (KAKENHI)
- Grant/Contract Number:
- AC52-07NA27344; JP19H05817; 19H05818; 19H05819
- OSTI ID:
- 2212867
- Report Number(s):
- LLNL-JRNL-857004; 1086148
- Journal Information:
- Journal of Solid State Chemistry, Vol. 329; ISSN 0022-4596
- Publisher:
- ElsevierCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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