Eur. Phys. J. AP 8, 111-121 (1999)
https://doi.org/10.1051/epjap:1999236

Effects of excess carbon and vibrational properties in ultrafine SiC powders

¹ Laboratoire de Physique de l'état condensé (UPRES-A CNRS 6087), Université du Maine, Faculté des Sciences, avenue Olivier Messiaen, 72085 Le Mans Cedex 09, France
² CEMES (UPR CNRS 8011), B.P. 4347, 29 rue Jeanne Marvig, 31055 Toulouse Cedex, France
³ CEA-DRECAM, Service des Photons Atomes et Molécules, CE Saclay, 91191 Gif-sur-Yvette Cedex, France

Corresponding author: kassiba@aviion.univ-lemans.fr

Received: 7 January 1999
Revised: 28 June 1999
Accepted: 31 August 1999
Published online: 15 September 1999

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 T_a = 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 T_a is discussed with respect to the powder composition and the interface effects where the carbon in excess seems to play a key role.