Structural transition in rare earth oxide clusters

Abstract

Size effects, such as structure transition, have been reported in small clusters of alkali halide compounds. We extend the study to rare earth sesquioxide (Gd(2)O(3)) clusters which are as ionic as the alkali halide compounds, but have a more complicated structure. In a clean and controlled environment (ultra high vacuum), such particles are well crystallized, facetted and tend to adopt a rhombic dodecahedron shape. This indicates the major role of highly ionic bonds in preserving the crystal lattice even at small sizes (a few lattice parameter). Based on both cathodo-luminescence and transmission electron microscopy, we report the existence of a structural transition from bcc to monoclinic at small sizes.

Controlled shape growth of Eu- or Tb-doped luminescent Gd2O3 colloidal nanocrystals

“…Although the main XRD peak (2θ ≈ 32.47 • ) of monoclinic Gd 2 O 3 (JCPDS file 43-1015) was seen in both samples, most of the monoclinic peaks overlapped with those from cubic Gd 2 O 3 (JCPDS file 43-1014), making it difficult to determine from XRD if a single or multiple phases were present. The uncertainty in the phase identification of such a tiny sized objects might be accepted if considering that the phase transition from cubic to monoclinic phase in rare earth oxide (e.g., Gd 2 O 3 ) clusters is size-dependent, and particularly occurs in the size range of 2-3 nm [32]. However, a relatively sharp monoclinic (002) peak was seen at 32.47 • from nanoplates, consistent with these planes being the face along which the stacks self-aligned.…”

Optimization of the synthesis of nanostructured Tb3+-doped Gd2O3 by in-situ luminescence following up

“…Such planes possess then a high surface energy which indicates that the formation of particles boundaries along (222) faces within the rods is certainly surface-energy driven. One can also notice that the (110) faces are neutral (no excess of charges) while the (222) faces are not [39]. Thus the (222) faces are not expected to be as stable as they are in the NaCl or CsCl structures which is an additional explanation to the organization observed.…”

Morphological and structural properties of InP/Gd2O3 nanowires grown by molecular beam epitaxy on silicon substrate

“…The Gd 2 O 3 nanocrystals were found to be cubic when grown by Low Energy Cluster Beam Deposition [32,34], SolGel [35] or growth in solution [36]. A possible transition from cubic to monoclinic structure have been identified for crystal diameter less than 2.3 nm [34], which is smaller than the size of the nanocrystals presented in this paper. However, the direct fabrication of monoclinic Gd 2 O 3 nanocrystals has been reported recently [37], using a chemical preparation technique.…”

“…However, due to the similar ionic radius between Gd and Eu, it was argued that the substitution did not affect the Gd 2 O 3 crystal structure [32]. The Gd 2 O 3 nanocrystals were found to be cubic when grown by Low Energy Cluster Beam Deposition [32,34], SolGel [35] or growth in solution [36]. A possible transition from cubic to monoclinic structure have been identified for crystal diameter less than 2.3 nm [34], which is smaller than the size of the nanocrystals presented in this paper.…”