Thermodynamic stability of elemental boron allotropes with varying numbers of interstitial atoms

Wataru Hayami; Takanobu Hiroto; Kohei Soga; Tadashi Ogitsu; Kaoru Kimura

doi:10.1016/j.jssc.2023.124407

論文 Thermodynamic stability of elemental boron allotropes with varying numbers of interstitial atoms

Wataru Hayami (National Institute for Materials Science) ; Takanobu Hiroto (National Institute for Materials Science) ; Kohei Soga ; Tadashi Ogitsu ; Kaoru Kimura

J. Solid State Chem. 329 (2024) 124407 MDR.pdf

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Wataru Hayami, Takanobu Hiroto, Kohei Soga, Tadashi Ogitsu, Kaoru Kimura. Thermodynamic stability of elemental boron allotropes with varying numbers of interstitial atoms. Journal of Solid State Chemistry. 2023, 329 (), 124407. https://doi.org/10.1016/j.jssc.2023.124407

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(abstract)

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. 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 beta-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 beta-rhombohedral boron samples. alpha-tetragonal boron is consistently most stable with 52 atom/cell and becomes unstable with more than 52 atoms/cell. Similar to beta-rhombohedral boron beta-tetragonal boron may undergo a phase transition between 192 and 190 atoms/cell configurations. However, the thermodynamic stability of pure beta-tetragonal boron has been questioned in comparison with other allotropes.

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