Energetics of titanium nitrides of composition Ti2N

The band structure and energetics of epsilon-Ti2N and delta'-Ti2N were calculated by means of the full-potential linearized augmented-plane-wave (FLAPW) method. In accordance with experiment, epsilon-Ti2N was found to be more stable than delta'-Ti2N. The transformation energy at 0 K was calculated as 9.35 kJ mol(-1). Relaxation of the Ti atoms stabilizes the delta'-phase and the relaxation energy of 28.75 kJ mol(-1) is rather high. A comparison with a former LAPW band-structure calculation that used a muffin-tin potential shows significant differences which are ascribed to the sensitivity of some very delocalized valence states to the approximations for the potential in the interstitial region. Thus, the importance of using a full potential for these compounds is stressed. A FLAPW calculation for the fictitious compound delta'-Ti2C furnishes qualitative explanations for the instability of the delta'-Ti2N structure for this substance.