  The 3-body crystallization diagrams of C/O/Ne ionic mixtures characteristic
of white dwarf interiors are examined within the framework of the
density-functional theory of freezing. The crystallization process is described
more accurately than in former calculations where the three-component system
was treated as an effective two-component mixture (Segretain et al. 1994). The
distillation process due to neon-crystallization is found to occur only for the
late stages of crystallization. At the beginning, the presence of neon plays
only a minor role and the phase diagram resembles a pure carbon-oxygen diagram.
The final phase diagram is found to exhibit an azeotropic point with a neon
concentration $x_{Ne}=0.22$, a carbon concentration $x_{C}=0.78$ and an oxygen
concentration $x_O=0$, so that during the distillation process, the fluid
crystallizes into a pure neon-carbon solid. The critical temperature is
$T_A=0.85\,T_C$, where $T_C$ is the pure carbon crystallization temperature. We
use this accurate phase diagram to calculate the total gravitational energy
released during white dwarf crystallization and the related time delay. The
final result yields $\Delta \tau \approx 2.6$ Gyr, among which about 20\% are
due to the neon-distillation process.
