| Three samples: titanium carbide TiC (sample I), titanium-tungsten carbide (Ti,W)C (sample II), and nanocrystalline TiC dispersed in a carbon matrix (sample III) have been selected for electrical conductivity measurements. The first two samples consisted of micron-size grains, while the third was a nanocrystalline TiC/C composite and was synthesized by a nonhydrolytic sol-gel process. All samples have been characterized by the X-ray diffraction (XRD), scanning microscopy, microanalysis (WDS and EDS), transmission electron microscopy (TEM) and electron diffraction techniques. For sample II the ratio of W:Ti atoms was equal to 0.3. The grain sizes in sample I and II were measured using the Fisher method and mean diameter of the grains was calculated to be below 10 µm. The TEM examination of the TiC particles in the sample III has showed that they were formed with an average crystalline size around 20 nm. XRD measurements of sample III have revealed that the lattice constant is smaller than observed for other titanium carbides TiCx· dc electrical conductivity studies have been made in the 80-330K temperature range. Samples I and II have shown a metallic behavior but with different slopes of the conductance vs. temperature dependence. Sample III at higher temperatures displayed a pronounced thermal hysteresis in dc conductivity. ac conductivity measurements have not shown any frequency dependence in the 1 kHz - 100 MHz range. |
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