The pressure-temperature phase and transformation diagram for carbon; updated through 1994 Review Article

In recent years, important advances in our understanding of the pressure-temperature phase and transformation diagram for carbon have occurred as a result of developments in both experimental and theoretical techniques. Graphite, diamond, liquid and vapor remain the major thermodynamically stable forms of carbon. However, due to the high activation energies for solid-state transformations and the specific effects of reaction paths, other metastable forms and a wide spectrum of complex hybrid forms may be generated, and possibly quenchedin, to survive metastably. This paper focuses primarily on developments since the last review of the carbon phase diagram published in 1989, but also includes references to the reliable older work. Some of the newer conclusions include the following: the Clapeyron slope of the diamond melting line, dTmdP, is positive; the liquid is metallic and there appears to be no evidence for a transformation between electrically conducting and non-conducting forms; melted droplets of carbon less than 0.2 μm in diameter quench to a giant fullerene structure even in the stability field of diamond; graphite transforms to a transparent phase on compression at room temperature; this phase reverts to graphite on decompression at this temperature from pressures as high as 100 GPa.