What Is The Crystal Structure Of Aluminium Dodecaboride?

Aluminum dodecaboride (AlB12) has a complex crystal structure that belongs to the rhombohedral space group R-3m. The unit cell of AlB12 consists of 13 boron atoms and one aluminum atom. The aluminum atom is located at the center of the unit cell, surrounded by a distorted icosahedron composed of twelve boron atoms.

The boron atoms are arranged in two types of clusters: six B12 icosahedra, each sharing a face with another, form a larger icosahedral cluster. These are interconnected through edge-sharing and vertex-sharing with six individual boron atoms, which fill the interstitial voids between the neighboring icosahedral clusters.

The crystal structure of AlB12 can be described as a three-dimensional network of covalent bonds between boron atoms, with aluminum atoms occupying the interstitial sites. The aluminum atom is highly distorted from an octahedral coordination, as it interacts strongly with the boron icosahedral structure around it.

This unique crystal structure gives AlB12 some remarkable physical properties, such as high hardness, thermal stability, and excellent electrical conductivity.