Heats of formation of interstitial compounds and their alloys

The bonding of compounds of the form RY in the NaCl structure is predominantly ionic, as shown by spectroscopic studies of charge transfer. A formula for the heats of formation of these compounds (R=Ti, Zr, Hf, V, Nb, Ta and Y=C, N, O) is constructed based on a modification of Pauling's electronegativity table. The formula yields good agreement with experiment, and is refined to yield more accurate values of the R electronegativities. The heat of formation of NbN is anomalously small, and this may be correlated with its high superconducting transition temperature. Miscibility gaps in the alloy systems R′_xR″_1?xC are discussed.