Intrinsic planar defects in diamond and the upper limit on its melting temperature

Abstract

Investigating melting curve of diamond is a challenging task both from experimental and theoretical points of view. Here we propose a simple method of calculation of the upper limit of diamond melting temperature, based on the study of planar defects in it. Accumulation of certain type of planar defects leads to softening of interatomic bonds and eventually to loss of shear rigidity of diamond and crystal disordering. The upper limit on melting temperature, defined in this work, is about 4750 K at ambient pressure and increases with pressure at the rate of 35 K/GPa. It appears, that experimentally established melting temperatures of diamond at the low pressure part of the phase diagram (at about 15 GPa) are close to the proposed upper limit on the melting temperature.