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Abstract 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 ZrCxexhibited diamond cubic symmetry with a supercell that consisted of eight (2 × 2 × 2) ZrCxunit 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 ZrCxpowders. Direct synthesis of ZrC0.6resulted in the partial ordering of carbon vacancies without the need for extended isothermal annealing as reported in previous experimental studies.
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Defect formation and migration in zirconium carbide under charge variation: A first‐principles study
Abstract Zirconium carbide (ZrC), a high‐performance refractory ceramic, exhibits complex defect dynamics that critically influence its behavior in extreme environments. In this work, we employ density functional theory (DFT) simulations to determine the formation energies and migration barriers of four defect types—isolated carbon vacancies, divacancies, Frenkel pairs, and Schottky pairs—across various charge states. The calculated formation energies reveal that isolated carbon vacancies are the most energetically favorable (1.13 eV), followed by Frenkel pairs (3.29 eV), while divacancies (6.86 eV) and Schottky pairs (8.29 eV) require higher formation energies, indicating their lower intrinsic concentrations. Isolated carbon vacancies exhibit the highest migration barrier (4.11 eV) in ZrC, with a modest increase to 4.13 eV upon adding one electron to 64‐atom supercell and a decrease to 4.06 eV with two electrons/64‐atom supercell—reflecting charge redistribution that stabilizes the local environment and weakens nearby Zr–C bonds. In contrast, Frenkel and Schottky pairs show barrier increases with electron doping and decreases with holes (ranging from 3.26 to 3.44 eV and 3.37 to 3.73 eV, respectively), while divacancies display increases (carbon vacancies: 2.69 to 2.93 eV; zirconium vacancies: 3.60 to 3.69 eV) upon electron addition. These results reveal the defect‐specific impact of charge carriers on mobility in ZrC, offering key insights for optimizing its performance in extreme environments.
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- Award ID(s):
- 2427926
- PAR ID:
- 10600233
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of the American Ceramic Society
- Volume:
- 108
- Issue:
- 9
- ISSN:
- 0002-7820
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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