Temperature Dependence of the EPR Spectra of the Nanocrystalline TiN and TiC Dispersed in a Carbon Matrix

Abstract

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.

Magnetic Study of Nanocrystalline TiB2, TiC, B4C Powders Doped to AISI 316L Austenitic Steel

“…Trivalent Ti 3+ complexes in nanocrystalline TiC/C systems were detected previously [10,11]. The addition of boron (B) to noncrystalline samples formed molybdenum-titaniumcarbide (Mo-Ti-C) system, significantly changed the ap- pearance and the temperature dependence of the FMR spectra of the Mo-Ti-C system, and increased the number of paramagnetic centers [10][11][12][13]. Boron is the element whose properties place it on the borderline between metals and non-metals (semimetallic).…”

“…Our interest in magnetic study of nanostructure materials began with the study of TiC and TiN nanoparticles in different matrices [10][11][12][13]. Titanium carbide (TiC x ) and titanium nitride (TiN x ) are very important technological materials because being refractory materials they have gained much attention due to their extraordinary hardness.…”

Ageing effect in nanocrystalline TiCx/C studied by EPR

“…The amplitude of the observed EPR signal decreases with temperature increase and the spectra are seen only at temperature below 120 K. Highly anisotropic EPR spectrum in the 335-375 mT range of magnetic field is observed that could be attributed to the Ti(III) ions. A very weak and narrow ( B = 0.17 mT) line centered at g eff = 2.0026(3) is apparently arising from the conduction electrons [8]. Fig.…”

“…The temperature dependence of electrical resistivity has shown a hysteresis connected with the disorder state inside titanium carbide through appearance of some trivalent titanium Ti(III) complexes, not existing in titanium nitride [7]. The electron paramagnetic resonance (EPR) study of titanium carbide and nitride has shown the presence of a very intense and narrow line arising from the conduction electrons [8,9]. Additionally, in titanium carbide the EPR spectrum * Corresponding author.…”

Paramagnetic centers in nanocrystalline TiC/C system

“…Moreover, titanium carbide dispersed in a carbon matrix displayed a rather peculiar thermal behavior of its electron paramagnetic resonance (EPR) spectra arising from conduction electrons [9,10]. On the other hand, previous studies have shown rather broad EPR spectra in TiC compounds indicative of high electrical conductivity and it was suggested that the electronic behavior is not dissimilar to that of bulk metals, in which the electrons exhibit fairly short spin-lattice relaxation times, giving rise to excessively broad lines which can not be observed with using the ordinary EPR spectrometers [11].…”