Competitive Growth of Scrutinyite (α-PbO₂) and Rutile Polymorphs of SnO₂ on All Orientations of Columbite CoNb₂O₆ Substrates

Abstract

Combinatorial substrate epitaxy (CSE) is used to investigate polymorph competition between metastable scrutinyite (α-PbO2) structured (s-) and stable rutile structured (r-) SnO2 during local epitaxial growth­ across orientation space on­ polycrystalline columbite (c‑) CoNb2O6 substrates. Growth occurs in a grain-over-grain fashion, where individual grains of c-CoNb2O6 support the growth of individual grains of SnO2. Both metastable s-SnO2 and stable r-SnO2 crystals are observed, each growing on specific ranges of substrate orientations and each having a single specific orientation relationship (OR) with substrate grains on which it grew. s-SnO2 adopts the unit-cell over unit-cell OR that can be expressed as the alignment of primary eutactic planes: (100) s* [001] s* ∥(100) c* [001] c* (where the * indicates the use of Pcnb setting). s-SnO2 grains grow on a slight majority of orientations and specifically on orientations inclined from the (010) pole of c*-CoNb2O6. r-SnO2 adopts an OR that can be expressed as the alignment of a secondary set of eutactic planes: (101) r [010] r ∥(010) c* [001] c* . r-SnO2 grows only on orientations close to the (010) pole of c*-CoNb2O6. The collected set of observations is discussed and rationalized with respect to the combination of misfit strain energies and cation packing interfacial energy penalties. We conclude that CSE should allow for the rational and computationally guided development of new materials adopting scrutinyite, rutile, and related structures.

Combinatorial substrate epitaxy investigation of polytypic growth of AEMnO3 (AE = Ca, Sr)

“…Phase and orientation for substrates and films were determined using EBSD in a Quanta 200 scanning electron microscope (SEM), as described elsewhere . Identical areas were mapped on the substrate and the films, respectively, before and after deposition.…”

“…Epitaxial stabilization is a method known to direct growth of a specific compound as a film in a particular crystal structure, using a supporting substrate as the template . Importantly, it has been used to grow metastable phases where other synthesis methods have failed . When optimized for epitaxial stabilization, nucleation of a bulk metastable phase is thermodynamically preferred due to a lower free energy of formation for its epitaxial nuclei, with important contributions from the film‐substrate interface and strain energies.…”

“…In CSE, polished polycrystalline substrates are used, which can be prepared in‐house for a wide range of structural families, and each grain of the substrate can be viewed as a single crystal with a unique orientation. Electron backscatter diffraction (EBSD) is used in CSE as a high‐throughput local structural probe to create phase and orientation maps across large areas of the substrate surface, as well as the deposited film . A single deposition of a film onto a polycrystalline substrate yields thousands of observations from which a broad understanding of phase stability and film‐substrate orientation relationships (ORs) can be developed.…”

“…A single deposition of a film onto a polycrystalline substrate yields thousands of observations from which a broad understanding of phase stability and film‐substrate orientation relationships (ORs) can be developed. For example, only a few ORs were found for epitaxial films on polycrystalline substrates across all of orientation space of the substrate . One common preferred epitaxial orientation (PEO) is called the eutactic OR, which aligns the eutactic (or nearly close‐packed) planes and directions between the film and substrate .…”

“…For example, only a few ORs were found for epitaxial films on polycrystalline substrates across all of orientation space of the substrate . One common preferred epitaxial orientation (PEO) is called the eutactic OR, which aligns the eutactic (or nearly close‐packed) planes and directions between the film and substrate . Furthermore, CSE has been used many times now to investigate polymorph stability, including anatase vs rutile TiO 2 and rutile vs scrutinyite SnO 2 .…”