  The interplay between the surface and domain wall phenomena in multiferroic
LaxBi1-xFeO3 in the vicinity of morphotropic phase transition is explored on
the atomic level. Scanning Transmission Electron Microscopy (STEM) has enabled
mapping of atomic structures of the material with picometer-level precision,
providing direct insight into the spatial distribution of the order parameters
in this material and their behavior at surfaces and interfaces. Here, we use
the thermodynamic Landau-Ginzburg-Devonshire (LGD) approach to explain the
emergence of spatially modulated phases (SMP) in La0.22Bi0.78FeO3 films, and
establish that the change of polarization gradient coefficients caused by
La-doping is the primary driving mechanisms. The suppression, or "melting", of
the SMP in the vicinity of the domain wall surface junction is observed
experimentally and simulated in the framework of LGD theory. The melting
originated from the system tendency to minimize electrostatic energy caused by
long-range stray electric fields outside the film and related depolarization
effects inside it. The observed behavior provides insight to the origin of
surface and interface behaviors in multiferroics.
