Ab-initio calculation of the elastic constants and thermal expansion coefficients of Laves phases

To develop new intermetallic materials for high-temperature applications, systematic knowledge of the elastic properties of crystalline phases are useful. For the Laves phases, specifically, it is often difficult and time-consuming to measure the elastic constants and thermal expansion coefficients directly. Accurate density-functional calculations are a promising alternative to supply this information. We present calculations of the elastic constants of the C15 Laves phases MAl2, where M=[Ca, Sc, Y, La] and MCr2 where M=[Ti, Zr, Ta, Nb], using a recently developed variant (NFP) of the linear muffin-tin orbital (LMTO) method. The method includes the full crystal potential and allows the computation of forces and thus the relaxation of the atomic positions as the unit cell is deformed. From the elastic strain tensor we estimate the bulk moduli, Youngʹs moduli, Poissonʹs ratios and sound velocities of polycrystalline samples. In addition, using the Debye–Grüneisen theory we obtain estimates for the Debye temperatures, specific heats and linear thermal expansion coefficients. Theoretical and experimental values are in reasonable agreement where experimental data are available. Overall, our results show that density-functional calculations can indeed substitute for explicit measurements for monocrystalline materials.