Synthesis of Novel High-Pressure Phases in the B–C–N–O–P System – BCNOP

The methodology included, in addition to theoretical calculations to predict high-pressure phases, advanced techniques for synthesis under extreme conditions, coupled with energy- and angle-dispersive synchrotron X-ray diffraction, and a full range of structural, physical and chemical characterization of the synthesized phases. The coherent combination of the interdisciplinary methods enabled the major advances of the project. Crystal structure prediction of novel high-pressure phases of the B-C-N-O-P system was performed using a new ab initio technique based on evolutionary algorithm USPEX. The formation of the high-pressure phases has been systematically studied over wide pressure and temperature ranges using laser-heated diamond anvil cells (up to 50 GPa and 3000 K), large-volume presses (up to 25 GPa and 2800 K) and X-ray diffraction with synchrotron radiation (at SOLEIL, ESRF and DESY). Structure and properties of the recovered samples were analyzed by powder X-ray diffraction (conventional and with synchrotron radiation), electron microscopy, Raman and infrared spectroscopy, hardness measurements, etc.

Synthesis and crystal structure of the new high-temperature dense pseudo-cubic boron allotrope, pc-B52.

Equilibrium phase diagram of boron that explains all thermodynamic aspects of the boron allotropy and significantly improves our understanding of the fifth element.

Equilibrium phase diagram of boron oxide B2O3 that represents only thermodynamic equilibria between crystalline and liquid states, not influenced by kinetic phenomena.

Theoretical prediction of two novel phases of the P-N system, metallic PN3 (Immm) and insulating PN2 (P2/m); and high-energy-density mixed polymeric carbon monoxide - nitrogen phase (Pbam).

Evolution of phase diagrams of the B-C and the B-B2O3 binary systems up to 24 GPa from phenomenological thermodynamics models with interaction parameters derived from our experimental data on HPHT phase equilibria.

Phase diagram of the B-N-O ternary system at pressures up to 5 GPa constructed by combining our data for binary sub-systems and phenomenological model describing ternary interactions.

Determination of the melting curves of hard refractory carbides (B4C and SiC) and boron phosphides (BP and B12P2) under pressure.

Electrical conductivity of melts of boron and its carbide (B4C), nitride (BN), and phosphide (BP) at pressures to 7.7 GPa and temperatures to 3500 K.

In-situ X-ray diffraction and Raman scattering study of cubic BP, orthorhombic B2O3 and rhombohedral BS to 50 GPa at 300 K.

p-V-T equation of state of superhard boron suboxide B6O up to 6 GPa and 2700 K: bulk modulus, thermal expansion and Anderson-Grüneisen parameter.

Development of the new combined detection system for energy- and angle-dispersive X-ray diffraction (CAESAR) under extreme conditions on beamline PSICHÉ, SOLEIL.

Development of new simple, efficient and low-cost methods of boron phosphides production by self-propagating high-temperature synthesis.

Development of new ultra-fast mechanochemical synthesis of the boron phosphides nanopowders.

Finally, at the end of the project, the thermodynamic and kinetic aspects as well as mechanisms of formation of new phases in the B-C-N-O-P system under high pressures and high temperatures are better understood. The results obtained shed light on the factors responsible for the phases formation of compounds of light elements, which are of great importance for high-pressure chemistry and materials science. These data will also help to develop principles of producing new advanced materials having enhanced thermal and chemical stability as compared with the existing ones that is of crucial importance for industry.

The project has already resulted in 24 scientific articles in peer-reviewed journals, 1 book chapter, 12 invited lectures and 18 oral & poster presentations at international and French conferences; as well as in 2 national and 1 international patents on new methods of boron phosphides' production. Several articles are in press or will be submitted in the near future. We are also waiting for the PCT extension of one national patent.

In the proposed research, the formation of the theoretically predicted novel binary and ternary high-pressure phases in the B-C-N-O-P system will be systematically studied over wide pressure and temperature ranges using laser-heated diamond anvil cells (up to 50 GPa and 3000 K), large-volume presses (up to 25 GPa and 2800 K) and X-ray diffraction with synchrotron radiation (SOLEIL, ESRF, HASYLAB-DESY). The structure and properties of the recovered samples will be investigated by powder X-ray diffraction (conventional and with synchrotron radiation), electron microscopy, EELS spectroscopy, Brillouin scattering, Raman spectroscopy, thermal analysis, hardness measurements, etc.
The overall scientific goals of the project are: (1) fundamental understanding of the physico-chemical phenomena occurring at high pressures and temperatures in the systems containing light elements and (2) systematic search for new superhard, refractory, superconducting, high energy density, etc. phases of the B-C-N-O-P system.
From the proposed research, the thermodynamic and kinetic aspects as well as mechanisms of formation of new binary and ternary phases in the B-C-N-O-P system under high pressures and high temperatures will be better understood. The results obtained should shed light on the factors responsible for the phase formation of compounds of light elements, which is of great importance for high-pressure chemistry and materials science. These data also will help to develop the principles of producing new advanced materials having enhanced thermal and chemical stability which is of particular importance for industry.