High-pressure study of graphite-like B–C phases

Abstract

The 300 K equations of state of graphite-like B–C phases with boron content from 0 to 50 at% have been studied using powder X-ray diffraction with synchrotron radiation up to 35 GPa. The compression axis moduli show the non-monotone dependence on boron content and strongly correlate with lattice parameters. The values of bulk moduli B ₀ vary from 17.5 (0.6) GPa (t-BC₄) to 30.7 (0.5) GPa (t-BC_1.5), while for turbostratic graphite B ₀=29.5 (1.0) GPa.

Keywords:

• graphite-like B–C phases
• high pressure
• equation of state
• synchrotron radiation

Acknowledgements

The authors thank Dr A. Derré for supplying us with the t-BC _x samples and Drs C. Lathe and D. Andrault for assistance in the high-pressure experiments. Measurements at ID30, ESRF were carried out during beamtime allocated to proposal HS-1693. Experiments at HASYLAB-DESY were supported by the GFZ-Potsdam under the MAX80 program. This work was financially supported by the Agence Nationale de la Recherche (grant ANR-05-BLAN-0141).

Notes

is the linear compressibility.

Due to the strong decrease in B’ from 12–15 to ∼6 in the framework of Birch–Murnaghan EOS already at relatively low pressures (i.e. ∼5 GPa), the corresponding values of B ₀′ can be strongly overestimated, especially in the case of the lack of experimental points. Using the Murnaghan EOS, we have obtained a mean value of over the pressure range studied.