Investigations on the Structural Properties of Silicon Hexaboride

(Investigations on the Structural Properties of Silicon Hexaboride)

Various investigations on the structural properties of silicon hexaboride have been carried out. They are mainly devoted to the investigation of doped or non-stochiometric SiB6 compounds. Several novel structures were discovered and optimized on the DFT level.

The amorphous phase of SiB6 has been reported to undergo pressure-induced structural transformation. The high-density amorphous phase consists of differently coordinated motifs and has a pentagonal pyramidal structure. This type of phase has a theoretical bandgap energy of 0.3 eV. It has a relatively low thermal expansion coefficient and high nuclear cross section for thermal neutrons. In addition, it exhibits ductile and semiconducting behavior.

There are three types of silicon hexaboride modifications: the d-SiB6 type, the g-SiB6 type, and the c-SiB6 type. These types of compounds are distinguished from each other by the degree of atom-atom coordination and the symmetry of the unit cell.

The d-SiB6 type is characterized by a layered-like structure, whereas the g-SiB6 type shows a cubic symmetry. Both types of compounds have a low thermal expansion coefficient and a moderate melting point. They have a brittle character. In the d-SiB6 type, there are four silicon atoms in six-fold coordination, whereas in the g-SiB6 type, there are five silicon atoms in four-fold coordination.

Using DFT methods, the d-SiB6-type and g-SiB6-type have been investigated. They have a definite density of states at the Fermi level. This confirms the thermodynamic stability of the compound. It also enables the analysis of the electronic structure of this phase.

(Investigations on the Structural Properties of Silicon Hexaboride)