Temperature dependence of the EPR spectra of the nanocrystalline TiN and TiC dispersed in a carbon matrix

Two powder samples: nanocrystalline titanium carbide (TiC) and titanium nitride (TiN) dispersed in a carbon matrix were synthesized by a nonhydrolytic sol-gel process. Both samples were characterized by the X-ray diffraction and transmission electron microscopy. The transmission electron microscopy examination of the TiC and TiN nanoparticles showed that their average crystalline size was about 20 nm. The temperature dependence of the EPR spectra for both samples was measured in 10 K to 200 K temperature range. A similar very narrow (about 0.2 mT) EPR line centered at g ≈ 2 (at room temperature) was recorded in both samples. The EPR line observed in both samples is arising from electron conductivity centers dispersed in the carbon matrix and it was fitted by Dysonian line shape. The temperature dependence of the EPR spectrum showed different behavior of these two samples. It is suggested that in the sample TiC/C multiwall carbon nanotubes are formed while in the sample TiN/C the graphite structure dominates.