Vacancy ordering in zirconium carbide with different carbon contents

Zirconium carbide (ZrCx) ceramics with different carbon contents were prepared by reactive hot-pressing. The rock-salt structure of ZrCx was the only phase detected by x-ray diffraction of the hot pressed ceramics. The relative densities of ZrCx decreased as carbon content increased, in general. The actual carbon contents were measured by completely oxidizing the ZrCx ceramics to ZrO2. For most compositions, the actual carbon contents were higher than nominal batched compositions, presumably due to carbon uptake from the graphite furnace and hot press dies. Selected area electron diffraction and neutron powder diffraction revealed the presence of carbon vacancy ordering in ZrCx for 0.6 < x < 0.75. Rietveld refinement of the neutron diffraction patterns determined that the crystal structure of the ordered phase was hexagonal, and the carbon site occupancies were higher than nominal batched carbon stoichiometry.