Transformations in phenylboronic acid at high pressures and temperatures

A recent report on obtaining the n-type conductivity in diamonds doped with boron–oxygen complexes in a metal solvent (X. Liu et al., PNAS 2019) stimulates interest in the synthesis of diamonds in heterohydrocarbon systems with oxygen and boron. The simultaneous effect of boron and oxygen heteroatoms on phase transitions in a hydrocarbon system is examined in phenylboronic acid C6H5B(OH)2 at pressures of 7–8.5 GPa and temperatures up to 1600 °C. At pressures of about 7 GPa and temperatures up to 1100 °C, the transformation of the precursor occurs through the stage of polymerization into a graphane-like phase with the subsequent formation of nanographite. Micro- and nanodiamonds are synthesized at 8.5 GPa and 1600 °C from the initial precursor and nanographite, which is a product of preliminary carbonization, respectively. Despite the presence of oxygen and boron in the growth system, the n-type conductivity in diamonds and nanographite is not detected. It is found that the degree of boron doping of diamond in hydrocarbon systems decreases in the presence of oxygen with a high chemical affinity to boron and that nanodiamonds in the carbonized product can be obtained when volatile components leave the system. © 2024