  The design of next generation \beta-type titanium implants requires detailed
knowledge of the relevant stable and metastable phases at temperatures where
metallurgical heat treatments can be performed. Recently, a standard
specification for surgical implant applications was established for Mo-Ti
alloys. However, the thermodynamic properties of this binary system are not
well known and two conflicting descriptions of the \beta-phase stability have
been presented in the literature. In this study, we use ab-initio calculations
to investigate the Mo-Ti phase diagram. These calculations predict that the
\beta-phase is stable over a wide concentration range, in qualitative agreement
with one of the reported phase diagrams. In addition, they predict
stoichiometric compounds, stable at temperatures below 3000C, which have not
yet been detected by experiments. The resulting solvus, which defines the
transition to the \beta-phase solid solution, therefore occurs at lower
temperatures and is more complex than previously anticipated.
