Effect of annealing on EPR spectra of Ti-Si-C-N samples

Two nanocrystalline samples of TiC+SiC+20%C (sample 1) and Si3N4+Si(C,N)+Ti(C,N)+1%C (sample 2) were prepared by non-hydrolytic sol-gel method. The latter sample was produced from sample 1, by subjecting it to additional annealing at high temperature. XRD measurements showed the presence of aggregates of cubic SiC+TiC nanoparticles (10 to 30 nm in size). In both samples, a very narrow electron paramagnetic resonance (EPR) line originating from localized magnetic centers was centered at geff2. At T = 130 K, we registered the linewidths DHpp = 1.41(2) G and DHpp = 2.92(2) G for the sample without and with thermal annealing, respectively. For the non-annealed sample, the resonance line was fitted by a Lorentzian line in the low temperature range, and by a Dysonian line above 70 K, which indicates a significant change in electrical conductivity. Therefore, thermal annealing can significantly improve the transport properties of samples. An analysis of the temperature dependence of the EPR parameters (g-factor, linewidth, integrated intensity) showed that thermal annealing has a significant impact on the reorientation processes of localized magnetic centers.