Carbon vacancy ordering in zirconium carbide powder

• Published in: Journal of the American Ceramic Society 2020-04, Vol.103 (4), p.2891-2898
• Main Authors: Zhou, Yue, Heitmann, Thomas W., Bohannan, Eric, Schaeperkoetter, Joseph C., Fahrenholtz, William G., Hilmas, Gregory E.
• Format: Article
• Language: English
• Subjects: Carbon; Carbon black; Chemical synthesis; Diamonds; Diffraction patterns; Electron diffraction; Isothermal annealing; Neutron diffraction; Neutrons; nonstoichiometry; Vacancies; vacancy ordering; Zirconium; Zirconium carbide; Zirconium hydrides
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/jace.16964

Ordered carbon vacancies were detected in zirconium carbide (ZrCx) powders that were synthesized by direct reaction. Zirconium hydride (ZrH2) and carbon black were used as starting powders with the molar ratio of ZrH2:C = 1:0.6. Powders were reacted at 1300°C or 2000°C. The major phase detected by x‐ray diffraction (XRD) was ZrCx. No excess carbon was observed by transmission electron microscopy (TEM) in powders synthesized at either temperature. Ordering of the carbon vacancies was identified by neutron powder diffraction (NPD) and further supported by selected area electron diffraction (SAED). The vacancies in carbon‐deficient ZrCx exhibited diamond cubic symmetry with a supercell that consisted of eight (2 × 2 × 2) ZrCx unit cells with the rock‐salt structure. Rietveld refinement of the neutron diffraction patterns revealed that the synthesis temperature did not have a significant effect on the degree of vacancy ordering in ZrCx powders. Direct synthesis of ZrC0.6 resulted in the partial ordering of carbon vacancies without the need for extended isothermal annealing as reported in previous experimental studies.