Structure and energetics of ZrC(100)||c-ZrO₂(001) interface: A combination of experiments, finite temperature molecular dynamics, periodic DFT and atomistic thermodynamic modeling

The oxidation process of ZrC is very important as it affects its initial excellent mechanical and physical properties. ZrC is an ultra-high temperature ceramic, but forms low refractory oxides at lower temperatures of 500–600 °C. To develop core/shell materials by coating the ZrC surface with another material that forms protective layers on ZrC and prevents it from oxidation (such as SiC), there is the need to study and characterize the oxidized layer surrounding ZrC particles. XPS, ToF-SIMS, TEM-ED and EDX analyses were used to investigate the covering oxidized layer, and polycrystalline ZrO₂(mainly cubic phase) was identified. Some traces of the tetragonal phase are observed to be present as shells around the ZrC particles with a thickness of about 4 nm on the average. Periodic DFT was subsequently used to characterize the interface formed between ZrC(100) and c-ZrO₂(001) phases. A strong interface was noticed mainly with charge transfer from Zr (c-ZrO₂ side) at the interface to O and C (ZrC side) atoms at the interface. The interfacial properties are local to only the first and second layers of ZrO₂, and not on the third and fourth layers of ZrO₂, as Bader charge analysis revealed substantial charge transfer at the interface region with no charge redistribution in the second ZrO₂ layer and subsequent bulk layers. The main physical quantity, ideal work of adhesion (W_ad), used to characterize the interface, remains quite constant for all ZrO₂ layers, and converges at three layers of ZrO₂. The interfacial bonds formed are observed to be stronger than the free surfaces in the corresponding ZrC and c-ZrO₂ used to generate the interface.