High pressure synthesis and investigations of properties of boron allotropes and boron carbide

This work aimed at the development of the high-pressure high-temperature (HPHT) synthesis of single crystals of boron allotropes and boron-rich compounds, which could be used further for precise investigations of their structures, properties, and behavior at extreme conditions. To summarize, the present work resulted in the HPHT synthesis of the first previously unknown non-icosahedral boron allotrope ζ-B. This finding confirmed earlier theoretical predictions, which stayed unproven for decades because of experimental challenges which couldn't be overcome until recently. Structural stability of α-B and β-B in the Mbar pressure range and B₁₃C₂ up to 68 GPa was experimentally proven. Accurate measurements of the unit cell and B₁₂ icosahedra volumes of the stoichiometric boron carbide B₁₃C₂ as a function of pressure led to conclusion that they undergo a similar reduction upon compression that is typical for covalently bonded solids. Neither 'molecular-like' nor 'inversed molecular-like' solid behavior upon compression was detected that has closed a long-standing scientific dispute. A comparison of the compressional behavior of B₁₃C₂ with that of α-B and γ-B allotropes and B₄C showed that it is determined by the types of bonding involved in the course of compression.