In the Go-Pt system, a simple cooling experiment can drive a sample ordered
in the cubic L1(2) structure (Cu3Au type) close to the two-phase region in
volving L1(2) and the tetragonal L1(0) (CuAu type) structure. Using transmi
ssion electron microscopy observations, we show that the antiphase boundari
es (APB's) in the L1(2), structure are decorated by the L1(0) structure and
that the L1(0) variant formed during this wetting process is related to th
e characteristics of the APE. The L1(0) tetragonal axis is normal to the di
splacement vector of the APE and the translational variant ensures the cont
inuity of the platinum-rich cubic planes between the bulk and the wetting s
tructure. To understand this peculiar wetting process, we develop different
theoretical approaches based on a microscopic Ising model on the fee latti
ce with interactions up to the second nearest neighbors. At 0 K, the model
accounts for the observed selectivity of the wetting process. Then, using a
mean field approach, our model predicts the wetting by the L1(0) structure
at finite temperature, with a selectivity similar to that observed in the
Go-Pt samples. Furthermore, the usual logarithmic divergence of the width o
f the wetting layer with respect to the excess free energy still holds. Fin
ally, we use a general phenomenological Landau approach, where the symmetri
es of the fee lattice and of the (vectorial) order parameter are taken into
account, to show that the width of the wetting layer is very sensitive to
the orientation of the APE. This phenomenological approach makes it clear a
lso that the wetting of the APE in the L1(2) structure by the L1(0) phase,
although observed here, is not unavoidable theoretically, which is not the
case when the relevant order parameter is scalar.