Compounds of the quaternary system Hf-Si-C-O are encountered in high-temperature ceramic composites after oxidation at elevated temperatures. Materials properties are dominated by the terminal binary phases, HfO2, SiO2, and SiC and by the ternary phase HfSiO4. However, intermediate compositions may play a crucial role in amorphous regions of the materials, at interfaces between crystalline phases, and during the temporal processes of oxidation and phase separation.
In this study, we present hypothetical crystalline models of quaternary Hf-Si-C-O compounds that approximate various stages and conditions of the system. Well-ordered structures of different compositions have been generated using the Ab-Initio Random Structure Search (AIRSS) algorithm and optimized within density functional theory.
We identify lowest energy structures and highlight trends in structural features. While no new stable structure is found, we nevertheless observe peculiar geometries with low excess energy; among these a low-energy interface between 2H-SiC and t-HfO2.