This would be very useful, considering that we do not have a high melting point solid that does not break under pressure.
Hafnium Carbide has the highest melting point out of all compounds consisting of only two elements (3900).
Thorium Oxide has the highest melting point out of all oxides (3390).
I don't know why I never heard of this. But I know the Formula is Ta4HfC5. Also, the melting point in Degrees Celsius is 3880. So adding Hafnium Carbide would be better, because all three have excellent conductivity and resistance to chemical attack, pressure and thermal shock.