Theoretical study of the elastic constants of off-stoichiometric alloys

To study theoretically mechanical properties of intermetallics by all electron band structure procedures one usually calculates these properties using the ideal crystal structure for the material. Here we have investigated the mechanical properties in non stoichiometric compounds. We have calculated the elastic tensor for NbHx and NbCr2-xVx as a function of composition x in order to see whether band structure methods can predict the right trend in the change of the elastic properties caused by defects. We present calculations of the elastic constants using a full-potential 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. Theoretical and experimental values for the elastic constants are in reasonable agreement where experimental data are available. Overall, our results show that density-functional calculations can indeed predict trends in the change of the elastic properties by alloying or degrading.