Abstract
In order to clarify the discrepancy of the phase diagram on boron
nitride as it is found in the literature we have made numerous in
situ diffraction experiments using synchrotron radiation. The conditions
were temperatures in the range of 1600?C and pressures up to 6.5
GPa. For the experiments diamond anvil squeezers and the MAX80 high-pressure/high-temperature
device installed at the DESY synchrotron facility in Hamburg/Germany
were used. We studied the transformation from hBN to cBN at 6.5 GPa/1200?C
and the backtransformation from cBN to hBN around 0.9 to 2 GPa. The
experiments included kinetics measurements. The experiments verified
the theoretical results by V. L. Solozhenko (1991, High Pressure
Res. 7, 201) and J. Maki et al. (1991, ?Proceedings II: International
Conference on New Diamonds Research and Technology?). Further on
the calculations for the equilibrium boundary between cBN and hBN
were repeated including uncertainties of the thermodynamic data.
The cubic phase, cBN, is definitely the stable phase, in contrast
to metastable diamond.
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