Defect Structure of Zirconium Carbide

Vacancy ordering in substoichiometric zirconium carbide: A review

“…Finally, Pakhomov theoretically examined defect structures in zirconium carbide for the purposes of understanding the shape of the homogeneity region in the phase diagram 58 . While Pakhomov's results provide an interesting exploration of the phase diagram topology, the proposed layered vacancy structures are not consistent with experimental observations, or the ordering observed in the ground state stable structures predicted via CE method or the USPEX EA.…”

“…The displacement of ions close to a vacancy has been explored experimentally by de Novion and Maurice 25 and theoretically by Råsander and Delin, 63 Pakhomov, 58 and Davey et al 43 . When an isolated carbon vacancy is present in stoichiometric zirconium carbide, the closest zirconium atoms are displaced away from the vacancy, and the nearest‐neighbor and next nearest‐neighbor carbon atoms contract towards the vacancy, as shown schematically in Figure 9A.…”

“…43 F I G U R E 9 Schematic of competing lattice distortion effects in the (001) plane from each vacancy in (A) an isolated vacancy, (B) first nearest-neighbor vacancy pair, (C) second nearest-neighbor vacancy pair, adapted from Davey et al 43 Blue, red, and yellow arrows show the displacement directions of the nearest-neighbor Zr atoms, first nearest-neighbor C atoms, and second nearest-neighbor C atoms, respectively. Reproduced from Davey et al 43 The displacement of ions close to a vacancy has been explored experimentally by de Novion and Maurice 25 and theoretically by Råsander and Delin, 63 Pakhomov, 58 and Davey et al 43 When an isolated carbon vacancy is present in stoichiometric zirconium carbide, the closest zirconium atoms are displaced away from the vacancy, and the nearest-neighbor and next nearest-neighbor carbon atoms contract towards the vacancy, as shown schematically in Figure 9A. This results in a net volume increase for an isolated vacancy, with vacancy formation volume calculated with full anharmonic accuracy up to the melting temperature by Mellan et al to be ∼13.2 Å/isolated vacancy, 65 which is consistent with calculations by Davey et al who additionally report the excess volume per vacancy compared to a carbon atom as just over 1 Å/isolated vacancy.…”