Extended Data Fig. 1. Oxide inclusions.

a, SEM image of (HfNbTiVZr)CN, contrast optimized to show intra-grain inclusions. b, segmentation into inclusions (red), grain boundaries (purple) and grains (green) using Weka⁹³ c, oxygen SEM- EDS map. Based on the segmentation in b we can compare the average intensity in the inclusion region of the O EDSmap in c and in Extended Data Fig. 4. The elements O (1.94), Hf (1.31) and Zr (1.26) are enriched in the inclusions, while the intensities of Ta (0.70), Ti (0.66), and V (0.66) are reduced compared to the grains. Overall, the small amount of oxide in the studied ceramics would mean that the compositional differences in the high-entropy carbonitride phases would be very small (i.e., less than 1 mol%) with the small amount of oxide present in thermodynamic equilibrium with the carbonitride.