Structural stability and mechanism of compression of stoichiometric $\mathrm{B_{13}C_2}$ up to 68GPa

Boron carbide is a ceramic material with unique properties widely used in numerous, including armor, applications. Its mechanical properties, mechanism of compression, and limits of stability are of both scientific and practical value. Here, we report the behavior of the stoichiometric boron carbide B$_{13}$C$_2$ studied on single crystals up to 68 GPa. As revealed by synchrotron X-ray diffraction, B$_{13}$C$_2$ maintains its crystal structure and does not undergo phase transitions. Accurate measurements of the unit cell and B$_{12}$ icosahedra volumes as a function of pressure led to conclusion that they reduce similarly upon compression that is typical for covalently bonded solids. A comparison of the compressional behavior of B$_{13}$C$_2$ with that of α–B, γ–B, and B$_4$C showed that it is determined by the types of bonding involved in the course of compression. Neither ‘molecular-like’ nor ‘inversed molecular-like’ solid behavior upon compression was detected that closes a long-standing scientific dispute