Uniaxial-Stress-Driven Transformation In Cold Compressed Glassy Carbon

We show that transformation of glassy carbon (GC) into a translucent superhard carbon phase by cold-compression is obtained in the presence of a uniaxial stress field. This transition accompanies with sp(2) to sp(3) bonding change in GC, and it is found that the uniaxial stress strongly favors this bonding transition. The transformation of GC causes photoluminescence and significantly increases light transmissivity. Upon decompression, the high pressure phase can be maintained under large uniaxial stress at a chamber pressure even down to similar to 10GPa. We discuss possible mechanisms of these transitions by a distinct bonding process that occurs in noncrystalline carbon.