Effects of excess carbon and vibrational properties in ultrafine SiC powders

Abstract

Structural and vibrational properties are investigated in SiC nanopowders synthesized by a CO2 laser pyrolysis of (SiH4, C2H2) gaseous mixture and thermally treated up to 1800 °C. The structural modifications of the SiC crystallites and the arrangement of the carbon in excess are monitored at different annealing stages. A critical behaviour is revealed in the powder annealed at Ta = 1500 °C through the features of the Raman spectra and the insulating-conductor transition. The significant electric conductivity (σ ≈ 0.05 S cm−1) which appears above Ta is discussed with respect to the powder composition and the interface effects where the carbon in excess seems to play a key role.