AlV${}_2$O${}_4$ thin films via in-situ interfacial topotaxy

Abstract

Conventional oxide epitaxy approaches face challenges when the oxidation conditions of constituent elements differ significantly. Here we demonstrate that V--O thin films can serve as solid-phase precursors for epitaxial AlV${}_2$O${}_4$, comprising a pyrochlore V${}^{2.5+}$ network coexisting with AlO${}_4$ tetrahedra within the spinel structure. The epitaxial AlV${}_2$O${}_4$/Al${}_2$O${}_3$ (0001) heterostructures are realized via interfacial topotactic transformation, involving V--O growth at a moderate temperature followed by in-situ ultra-high-temperature post-annealing to drive a reaction with the Al${}_2$O${}_3$ substrate. Transmission electron microscopy and temperature-dependent X-ray diffraction analyses reveal excellent structural characteristics that closely reproduce the known charge-ordering transition. This study presents a novel approach to realizing epitaxial structures with convoluted oxidation states where thermodynamic and kinetic barriers would otherwise limit synthesizability.