SiC/HfyTa1-yCxN1-x/C ceramic nanocomposites with HfyTa1-yCxN1-x-carbon core-shell nanostructure and the influence of the carbon-shell thickness on electrical properties

Dense monolithic SiC/HfyTa1-yCxN1-x/C (y = 0, 0.2 and 0.7) ceramic nanocomposites were prepared upon spark plasma sintering of amorphous SiHfTaC(N) ceramic powders which were synthesized from single-source-precursors. The microstructural evolution of the ceramic powders was investigated using elemental analysis, X-ray diffraction, Raman spectroscopy and transmission electron microscopy (TEM). The results reveal that the powdered and dense monoliths of SiC/HfyTa1-yCxN1-x/C ceramic nanocomposites annealed at T >= 1700 degrees C and at 2200 degrees C, respectively, are characterized by the presence of a homogeneous dispersion of HfyTa1-yCxN1-x-carbon core-shell nanoparticles within a beta-SiC matrix. Hf/Ta atomic ratios (or y values) of the in situ generated HfyTa1-yCxN1-x-carbon core-shell nanoparticles can be controlled precisely by molecular tailoring of the preceramic precursors, which further tunes the thickness of the in situ formed carbon shell. Interestingly, with increasing the value y the thickness of the carbon shell increases, while the electrical conductivity of the dense monolithic SiC/HfyTa1-yCxN1-x/C (y = 0, 0.2 and 0.7) nanocomposites significantly reduces. The unique HfyTa1-yCxN1-x-carbon core-shell nanostructure opens a new strategy towards tailoring the electrical conductivity of SiC/HfyTa1-yCxN1-x/C nanocomposites for potential electromagnetic applications in harsh environments.