The effects of high-pressure high-temperature annealing upon the dissociation of N aggregates was investigated, with special attention being paid to the effect of pressure. When the pressure-temperature conditions were above the diamond/graphite equilibrium line, an activation energy of 5.6eV was estimated, from the Arrhenius plot of the dissociation rate of A centers, by assuming that the dissociation reaction of the A centers obeyed first-order kinetics. A second estimate for the binding energy of the A centers, derived from the equilibrium concentrations of A centers and C centers at 3 different temperatures, gave a value of 7.66eV. The dissociation rate of A centers was enhanced by a factor of about 10 when the pressure-temperature point during high-pressure high-temperature annealing was located within the stable graphite region of the C phase diagram.

The Influence of Pressure on High-Pressure, High-Temperature Annealing of Type Ia Diamond. F.De Weerdt, A.T.Collins: Diamond and Related Materials, 2003, 12[3-7], 507-10