A combined experimental and theoretical study was made, of grain boundaries in polycrystalline diamond, aimed at achieving the conditions under which grain boundaries were equilibrated. Raman spectra of compacted at high-pressure and high-temperature diamond powders permitted the identification of signals from sp2-bonded atoms, in addition to a strong peak at 1332/cm, corresponding to sp3-bonded carbon. To verify the present interpretation of the experiment, Σ5 (001) twist grain boundaries of polycrystalline diamond were studied by means of molecular dynamics simulations using the technique proposed by von Alfthan et al. (2006)]. It was found that grain-boundary (GB) configurations, from which one atom was removed, had a significantly lower energy compared to those obtained with conventional techniques. These calculated GBs were highly ordered, a few monolayers thick, in agreement with experimental observations, and were primarily sp2 bonded. This paper underlines the importance of varying the number of atoms within GBs in molecular dynamics simulations to correctly predict the grain-boundary ground-state structure.

Missing-Atom Structure of Diamond Σ5 (001) Twist Grain Boundary. P.Steneteg, V.Chirita, N.Dubrovinskaia, L.Dubrovinsky, I.A.Abrikosov: Physical Review B, 2011, 84[14], 144112