Hafnium carbonitride
Hafnium carbonitride (HfCN) is a highly refractory mixed anion ceramic compound composed of hafnium, carbon and nitrogen. Hafnium carbonitride's crystal structure is resistant to temperatures as high as 4,200 °C (7,590 °F). Under standard conditions it is the most heat-resistant material known, as no other known substance has a higher melting point. In 2015, atomistic simulations predicted that a Hf-C-N material could have a melting point exceeding Ta4Hf1C5 and hafnium carbide by 200 °C. This would later be proven in experimental testing conducted in 2020 by the National University of Science and Technology (NUST) in Moscow. Samples of both hafnium carbide and hafnium carbonitride were tested in the same environment in which hafnium carbonitride was shown to have a melting point exceeding 4,000 °C, higher than that of hafnium carbide (3,958 °C). More precise testing has yet to be conducted to determine the substance's exact melting point. References

Hafnium compounds
Carbides
Nitrides