Estimation of the critical radius for the nucleation of the c54 phase in c49 tisi2 role of the difference in density

We discuss the rather scattered measurements of the lattice parameters for C49 TiSi2, which are reported in literature, along with new and accurate X-ray diffraction measurements and ab-initio calculations. Both agree in indicating that the density of the metastable C49 structure cannot be much smaller than the one for the polymorphic C54 phase, as it is commonly reported. We conclude by demonstrating that only in the case of such a smaller difference in density between the two phases, the elastic strain contribution to the nucleation energy of the C54 structure in the C49 matrix can be neglected. The estimation of the critical radius strongly depends on this issue.