Nanoscaffold WO3 by Kinetically Controlled Polymorphism

Several metastable polymorphs, diverse crystal structures with the same chemical formula, could be accessed through epitaxial interfaces with low energy between epitaxial film and symmetry-matched substrates. Here, we fabricated tungsten oxide (WO3) nanoscaffolds composed of hexagonal WO3 (h-WO3)/monoclinic WO3 (m-WO3) polymorphs, and modulated the proportions of these phases by tuning the W arrival rate during epitaxial growth. The WO3 nanoscaffold is vertically aligned with coherent interphase boundaries between h-WO3 and m-WO3; this structure leads to the persistence of h-WO3 despite its metastable characteristic. The coherent interphase boundaries give rise to the unexpected six-fold m-WO3 phases and a distinct lattice response with intercalated hydrogen defects. This WO3 nanoscaffold with different fractions of two polymorphs would be a good model system to systematically study intercalation chemistry and its application with WO3 polymorphs.