I calculated Standard molar entropy of the Ti3AlC2 phase from Standard entropies of formation. It works. Thank you Luis - Felipe Velázquez - León.

The Ti3AlC2 molar formula can, in principle, be seen as corresponding to a solid solution based on titanium aluminide and titanium carbide: TiAl·2(TiC). By considering the binary system AnBm, with A ≡ TiAl and B ≡ TiC, it could be possible to estimate the partial molar entropies of solution from the differentiation of a plot correlating the available entropy data for this system; if indeed can be found reported. We may want to rely also on the Gibbs-Duhem relationship (for entropy), to better ensure the thermodynamic consistency of the differentiation procedure. The required entropy data could be then approximately derived, after the partial molar entropies of both components, as can be found discussed in many thermodynamic textbooks.