A new method has been proposed for the synthesis of nano- and microdiamonds with various contents of luminescent silicon-vacancy (Si-V) and nitrogen-vacancy (N-V) centers at high static pressures in...

A number of metastable ordered and disordered carbon phases have been prepared from fullerite ${\mathrm{C}}_{60}$ by heating to different temperatures at 12.5 GPa and subsequent quenching to ambient conditions. We studied the structure, Raman spectra, and hardness of the phases obtained. The increase of synthesis temperature up to 500 °C leads to a gradual three-dimensional polymerization and subsequent formation of a disordered network with a high share of ${\mathrm{sp}}^3$ sites. Further increase of the synthesis temperature leads to the formation of graphitelike clusters and then crystallization of graphite and diamond at $T\sim 900°\mathrm{C}.$ The structure of the polymer phases was identified as fcc, the lattice parameter value decreasing down to $\sim 11.6\AA$ with increase of synthesis temperature. A model of three-dimensional polymerization explaining the observed structural modification is proposed. The model allows one to calculate the share of covalently bonded molecules and describes the change of mechanical properties of polymeric phases in terms of rigidity percolation. Experimental results obtained for strongly polymerized states which favor a polymerization mechanism, other than $[2+2]$ cycloaddition are discussed.

We measured the Raman spectra of ferromagnetic, nearly half-metallic, CoS2 over a broad temperature range. All five Raman active modes Ag, Eg, Tg(1), Tg(2) and Tg(3) were observed. The magnetic ordering is indicated by a change of the temperature dependences of the frequency and the line width of Ag and Tg(2) modes at the Curie point. The temperature dependence of the frequencies and line widths of the Ag, Eg, Tg(1), Tg(2) modes in the paramagnetic phase can be described in the framework of the Klemens approach. Hardening of the Tg(2), Tg(1) and Ag modes on cooling can be unambiguously seen in the ferromagnetic phase. The line widths of Tg(2) and Ag modes behave in a natural way at low exciting laser powers (they decrease with decreasing temperature) in the ferromagnetic phase. At high exciting laser powers the corresponding line widths increase as temperature decreases below the Curie temperature. Then, as will be shown, the line width of the Ag mode reaches a maximum at about 80 K. Tentative explanations of some of the observed effects are given, taking into account the nearly half-metallic nature of CoS2.