Phase diagram of carbon

Abstract We have investigated a transition of graphite to diamond and diamond phase stability under high-pressure conditions. Graphite and diamond samples were subjected to pressure and shear deformation in the range from 25 GPa to 130 GPa. We propose a new phase diagram of carbon. The diagram includes a diamond instability zone in the pressure range from 55 to 115 GPa. It has been experimentally proved that diamond formation ceases in the pressure range from 55 to 115 GPa, while the already formed diamonds turn into carbon onions