On Bulk Modulus of Superhard 3D Polymers of Carbon Nanocluster

New superhard phase of single wall carbon nanotube (SP-SWNT) has been compared experimentally with 3D polymeric phases of analogous carbon cluster - fullerene C60 (both SWNT and C60 composed from curved graphene sheets). Mechanical properties of material composed from the polymerized clusters are determined by properties of the cluster. The 3D carbon nanocluster polymers were studied both in situ under pressure in a shear diamond anvil cell and after pressure release. Information about bulk modulus was derived from the pressure dependence for the phonon mode in high-energy range of the Raman spectra (i.e. the band 1594 cm-1 for SP-SWNT and 1570 cm-1 for 3D polymer of C60 ). This mode is similar for both materials: it is the bond-stretching mode of pair of carbon sp2 atoms, it is building bond for the clusters and in general it does not require the presence of graphitic structure and lies in the range 1500-1630 cm-1. In present study the Gruneisen parameter for 3D fullerite polymer was estimated experimentally using available experimental and theoretical data for bulk modulus of ultrahard fullerite (540 to 800 GPa depending on structure and synthesis conditions). The reasonable value for the fullerite Gruneisen parameter is the same as for the graphene sheet (1.1). The same value was used for the present estimation of bulk modulus of SP-SWNT (465 GPa). The value is close to diamond and consistent with theoretical calculations 420 GPa (L.A. Chernozatonskii et all. JETP Letters, 74, 467 (2001)). In addition to high bulk modulus SP-SWNT reveals superhard properties: its hardness (62 to 150 GPa) belongs to the range between cubic BN and diamond. Self-consistency of the experimental data and their correspondence with theoretical calculations gives base for an estimation and prediction of mechanical properties of new carbon nanocluster-based polymeric materials.