On the stoichiometry of zirconium carbide

The dependencies of the enhanced thermomechanical properties of zirconium carbide (ZrC_x) with sample purity and stoichiometry are still not understood due to discrepancies in the literature. Multiple researchers have recently reported a linear relation between the carbon to zirconium atomic ratio (C/Zr) and the lattice parameter, in contrast with a more established relationship that suggests that the lattice parameter value attains a maximum value at a C/Zr ~ 0.83. In this study, the relationship between C/Zr atomic ratio and the lattice parameter is critically assessed: it is found that recent studies reporting the thermophysical properties of ZrC_x have unintentionally produced and characterised samples containing zirconium oxycarbide. To avoid such erroneous characterization of ZrC_x thermophysical properties in the future, we propose a method for the accurate measurement of the stoichiometry of ZrC_x using three independent experimental techniques, namely: elemental analysis, thermogravimetric analysis and nuclear magnetic resonance spectroscopy. Although a large scatter in the results (ΔC/Zr = 0.07) from these different techniques was found when used independently, when combining the techniques together consistent values of x in ZrC_x were obtained.