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.

tags: semiconductor semiconductor material