Vacancies in zirconium carbide

Zirconium carbide is an ultra-high temperature ceramic with a melting point of 3700 K, which makes it extremely useful in the aerospace and nuclear industries due to its strength at extremely high temperatures. It is stable across a wide range of stoichiometry, facilitated by significant numbers of carbon vacancies, and many of its thermodynamic and mechanical properties are strongly affected by composition, making it an ideal candidate for creating tunable ceramics for a given application. However, the properties are determined not only by the number of vacancies, but also by their arrangement. Theoretical investigations predict a strong tendency towards vacancy ordering at low temperature, including self-assembly of vacancies into characteristic structures. Such vacancy ordering has been intermittently experimentally observed, but fabrication of ordered zirconium carbides remains a significant challenge. This presentation will review the nature of vacancy ordering in zirconium carbide and discuss possible explanations for the challenges in fabrication of ordered phases.