The existence of anti-phase boundaries (APBs) in defective crystalline materials

The existence of anti-phase domain boundaries (APBs) in polycrystalline materials is usually established by electron microscopic techniques (SEM/TEM) [1] and is also discussed in diffraction data analyses.[2]


I don’t have a good familiarity with TEM/SEM (and I’m very open to be educated here) but it doesn’t seem convincing enough to look at some microscopic images with atomic level resolution where APBs are found as a straight line (or arbitrarily curved line as in Figure 7 in ref. 1) forming a boundary/wall between the two domains in the same particles, while there is no disorderliness of any sort around and away from the APB.


The reason I’m raising this point is that particle surface is usually more disordered than any kind of defects in the bulk. In fact, it’s even well established that the surface of solid particles behave more or less like a liquid layer [3], and the smaller the particle size the thicker the liquid layer at the surface. And yet, in the TEM images of nanoparticles that I have seen in some articles there is(are) only the APB(s) visible, and no sign of the bigger unavoidable inherent surface disorder.


Is it possibly due to the fact that in TEM, the electrons pass through the particles and form an image which influenced by the bulk of the particle? If so, why then the rest of the atomic arrangements within the domains look nearly perfect (i.e. as if it’s a single layer of pointy ordered atoms)?


And as for the diffraction data, APBs affect some of the reflections selectively but usually there are different broadening contributions which make it challenging to disentangle. Nevertheless, at least the existence of planar defects like APBs is indicated in the diffraction patterns.


Any input would be appreciated.


1. Article: Antiphase Boundary Defects in Strontium Doped Lanthanum Scandate (M. V. Ananyev, Phys. Status Solidi B, 259: 2100376)
2. Article: Signature of antiphase boundaries in iron oxide nanoparticles (T. Köhler et al, J. Appl. Cryst. (2021). 54, 1719-1729)
3. Article: Observation of Surface Melting (Joost W. M. et al, Phys. Rev. Lett. 54, 134)


