Possibility of semiconducting quasicrystal in boron-rich solids - cohesive energy calculation and transformation from amorphous phase

Abstract

Boron-rich solids are great candidates for a semiconducting quasicrystal because they have various semiconducting crystalline structures with icosahedral clusters (B12). Analyzing the crystalline structure of α- and β-rhombohedral boron as an approximant structure of quasicrystal, the atomic structure of two unit cells (prolate and oblate rhombohedra) of the icosahedral quasicrystal are constructed. The cohesive energies of the α-, β-boron and α-boron type quasicrystal are estimated using molecular orbital total energy calculation. According to the calculation, the realization of α-boron type quasicrystal is expected. A neutral B12H12 icosahedral cluster is distorted to a cubic or rhombohedral one by the Jahn-Teller effect. The distortions of B12 cluster in the K2B12H12 and β-rhombohedral boron have the same signs as the lowest energy distortions in the calculation. Among the α-rhombohedral type structures, the distortion of B12 is correlated with the rhombohedral axis angle. The angle is close to the icosahedral angle and the distortion is smallest around 10 at% of carbon in B4C structure. Search for semiconducting quasicrystal has been done experimentally in the B-C system. A meta-stable phase has been found in the annealing process of the B100-xCx (x = 3, 5 and 7) amorphous phases.