Abstract
Selectively modulating the sublattices in 3D transition metal oxides via strains could tailor the electronic configurations with emerging anomalous properties, which provides new platforms for fundamental researches as well as designs of devices. Here, we report tailoring the oxygen octahedral sublattices in vanadium dioxide (VO2) thin films by anisotropic in-plane strains, and the observation of in-plane orientation-dependent metal–insulator transition. Through multimodal characterizations based on high-resolution X-ray diffraction, electrical transport measurements, and polarization-dependent X-ray absorption spectroscopy at different temperatures, we demonstrate that nonequal strains were successfully induced along A and B oxygen octahedral chains in VO2 films via a special design of epitaxial growth on vicinal substrates. The V 3d1 orbital configurations are modulated in the two oxygen octahedral chains, resulting in in-plane orientation-dependent metal–insulator transition behaviors such as reduced hysteresis width and anisotropic phase transition temperature. This work provides new fundamental insights on metal–insulator transitions, and more importantly, opens up new opportunities for material and device developments
Highlights
For some 3D transition metal oxides, sublattices with different spatial symmetries often coexist in their crystal lattices, such as in Fe3O4, CoFe2O4, Vanadium dioxide (VO2), and some superconductor cuprates crystal lattices
The epitaxial relationship between the films and the anisotropic in-plane strains on the VO2 lattice is the ability of tailoring the apical V–O bond length of the sublattices in the different octahedral chains separately
A possible mechanism for the conductivity anisotropy is the striplike phase domain structure generated by the phase separation during the phase transition in the film
Summary
Exploring exotic physical properties in 3D transition metal oxide films by using epitaxial elastic strains is a popular way in materials science. Strain, as a tool of modifying the crystal lattice of the oxide films, can simultaneously modify the interaction between charge, orbital and spin degrees of freedom, which are strongly related to the physical properties of materials. For some 3D transition metal oxides, sublattices with different spatial symmetries often coexist in their crystal lattices, such as in Fe3O4, CoFe2O4, Vanadium dioxide (VO2), and some superconductor cuprates crystal lattices. These sublattices, including oxygen octahedral, oxygen tetrahedron, and oxygen dodecahedron, are fundamental functional unit cells of oxides. For some 3D transition metal oxides, sublattices with different spatial symmetries often coexist in their crystal lattices, such as in Fe3O4, CoFe2O4, Vanadium dioxide (VO2), and some superconductor cuprates crystal lattices.. For some 3D transition metal oxides, sublattices with different spatial symmetries often coexist in their crystal lattices, such as in Fe3O4, CoFe2O4, Vanadium dioxide (VO2), and some superconductor cuprates crystal lattices.3,6,7 These sublattices, including oxygen octahedral, oxygen tetrahedron, and oxygen dodecahedron, are fundamental functional unit cells of oxides. Knowledge on correlation between the spatial symmetries of the sublattice unit cells and the symmetries of the charge, orbital and spin degrees of freedom of the 3D electrons inhabited in them, can provide a knob to tailor the sublattice of the 3D transition metal oxides using strain and to explore novel physical properties for practical applications
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