Mechanism of the structural phase transformations in epitaxial YHx switchable mirrors

Abstract

Geometric-shape-dependent structural transition behavior in (110) SrRuO3 epitaxial thin films Structure and strain relaxation mechanisms of ultrathin epitaxial Pr 2 O 3 films on Si(111) J. Appl. Phys. 97, 074906 (2005); 10.1063/1.1883304Switchable yttrium-hydride mirrors grown on CaF 2 (111): A x-ray photoelectron spectroscopy and diffraction studyThe detailed mechanisms of the structural phase transformations that occur in epitaxial Y-hydride switchable mirrors are revealed with high resolution transmission electron microscopy ͑both cross sectional and plan view͒. The triangular ridge network that develops in Y prior to the ␣-␤ transformation is a result of ͕101 2͖ deformation twinning. The basal plane that is originally parallel to the film/substrate interface is rotated by twinning over 5.6°and transformed into a prismatic plane and similarly the prismatic plane is transformed into a basal plane giving a final crystal reorientation for the ridge of 95.6°. After transformation to ␤, nearly vertical ⌺3͕111͖ twin boundaries arise in the ridges. In contrast, horizontal twin boundaries develop in the ␤ domains to prevent macroscopic shape changes. Inbetween the two twin variants within the domains, Shockley partial dislocations are persistently present, which enable efficient reversible ␤-␥ switching of the mirror.

Electrical and optical properties of epitaxial YHx switchable mirrors

“…[23]). This suggests that ridges contribute to the electrical transport properties of the as-deposited epitaxial Y film, since they are crystalline with the c-axis situated in-plane of the film [9]. Upon H absorption, the anisotropy ratio η(T ) increases (see in Table 2).…”

“…Using transmission electron microscopy (TEM), Kooi et al showed that the ridges are crystalline with the caxis almost in-plane [9]. They result from {1 0 1 2} deformation twinning [9]. Remarkably, the ridges act as a barrier for lateral H diffusion and as a sort of microscopic lubricant for the domain switching.…”

“…More ridges are formed during the ␣-␤ and ␤-␥ transformations upon H absorption [8]. Using transmission electron microscopy (TEM), Kooi et al showed that the ridges are crystalline with the caxis almost in-plane [9]. They result from {1 0 1 2} deformation twinning [9].…”

Thin‐Film Metal Hydrides

“…Here, the stress is relaxed along specific crystallographic planes resulting in characteristic morphology changes (triangles, see Figure 7). [84,10,85] At lower stress and strong adhesion, the stress is elastically relaxed. We will discuss first this case of strong adhesion, where the film stays attached to the substrate and the morphology remains basically unchanged (elastic strain relaxation), and then discuss the case of weak adhesion.…”

“…[23] It is at least a showing the interface between metallic yttrium, yttrium dihydride and yttrium trihydride. Although the large volume expansion causes significant morphology changes (so-called Manhattan structure, [84,10,85] ) the thin film remains intact (the figure is taken from ref. [47]).…”