Main interaction is the formation energy of BCC γ(U,Mo) disordered phase

In the aim of emphasizing the role of bonding energy between atoms in the decomposition of the metastable gamma phase and the solubility of third elements in U-Mo alloy, we decided to evaluate the thermodynamic functions of the binary U-Mo and ternary U-Mo-X systems by using first principles calculated total energies in a cluster expansion method. In the present study, we performed first-principles electronic calculations of 10 totally relaxed BCC-based ordered U-Mo structures. Then, we decided which clusters should be retained in the cluster expansion of the thermodynamic functions comparing their performance to reproduce the experimental equilibrium phase diagram. Finally, we discussed the contribution of the multisite interactions in the proper description of the alloy energetic. Interaction of three bodies has proved to play a fundamental role in stabilization of gamma phase, giving at the same time a useful tool for predicting ternary behavior. (author)