A potentially useful high-temperature intermetallic compound ${\mathrm{Ti}}_3$Al is investigated theoretically by the self-consistent linear muffin-tin orbitals (LMTO) and full-potential linearized augmented-plane-wave (FLAPW) methods within the local-density approximation. Structural properties were calculated for the naturally observed structure, D$0_{19}$, and for two other similar structures, D$0_{22}$ and L$1_2$. The LMTO-calculated Wigner-Seitz radii are 2.98 a.u. for all three structures, in excellent agreement with the experimental value (2.99 a.u.) of the observed D$0_{19}$ structure, while the values from the FLAPW method are 2.94 a.u. for the three structures, showing an agreement within about 2%. The calculated formation energies are 0.29, 0.27, and 0.29 eV/atom by the LMTO, and 0.28, 0.25, and 0.27 eV/atom by the FLAPW for the D$0_{19}$, D$0_{22}$, and L$1_2$ structures, respectively. The calculated bulk moduli are 1.2 Mbar for all the phases done by the LMTO and FLAPW except the D$0_{19}$ phase from the LMTO calculations, where the value is 1.3 Mbar. These calculated formation energies and bulk moduli agree well (to 10%) with experimental data. The FLAPW-calculated c/a ratio for the D$0_{19}$ and D$0_{22}$ structures are 0.807 and 2.131, respectively. The value for the D$0_{19}$ structure is within 1% of the observed value (0.8007) and the value for the D$0_{22}$ structure is significantly lower than the observed value (2.234) for ${\mathrm{TiAl}}_3$. Charge-density plots for D$0_{19}$ and L$1_2$ show quite localized charge distributions in both phases. The covalent character of the bonding is not significant, which may be a good sign for ways to improve its poor ductility.

• Received 8 March 1990

DOI:https://doi.org/10.1103/PhysRevB.43.1940