| Jan 25, 2022 |
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(Nanowerk News) Tohoku University researchers have observed a rare change in the structure of a mineral-like crystal that, if controlled, could lead to the development of new functional materials.
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The findings were reported in the Journal of the American Chemical Society (“Cation Dimerization in a 3d1 honeycomb lattice system”).
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| The crystal structure of ilmenite-type magnesium vanadate (MgVO3). The yellow line shows the honeycomb lattice. The thick lines indicate the location of V-V dimers. The crystal structure was drawn using VESTA-3 software. (Image: Hajime Yamamoto)
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Altering the atomic arrangements within materials can change their magnetic, electrical and optical properties. For instance, the pairing of positively charged cations in quasi one-dimensional crystals, such as vanadium dioxide (VO2), creates ‘covalent’ bonds, which can change the material’s electronic state and thus its conductivity.
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Until the latest Tohoku University study, however, scientists had only observed some examples of this so-called ‘cation dimerization’ in 3d transition metals with honeycomb lattice systems. 3d transition metals have specific properties and electrons that move about in the 3d orbital surrounding the atom.
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“Our findings will provide fundamental knowledge that will lead to the development of new functional materials,” says Tohoku University materials scientist Hajime Yamamoto.
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Yamamoto and his colleagues at Tohoku University and Osaka Prefecture University used high pressure to synthesize the simple oxide ilmenite-type magnesium vanadium trioxide (MgVO3), mimicking the conditions of mineral formation deep in the Earth’s core.
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The team then used synchrotron X-ray experiments to analyse the crystal’s structure and found that its honeycomb lattice developed vanadium-vanadium (V-V) dimers arranged in a ladder-like pattern at temperatures below 500 kelvin (227 °C). Interestingly, the team also observed a magnetic to non-magnetic transition in the crystal’s properties when the temperature fell below 600K.
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| A schematic of the honeycomb lattice (vanadium ions) and V−V dimers in ilmenite-type magnesium vanadate (MgVO3). The red arrows show the electronic spins.(Image: Hajime Yamamoto)
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The team next plans to explore the control of the V-V dimer state with magnetic fields and pressure. “We might be able to use this to create new magnetic or electrical functions in this and similar materials,” says Yamamoto.
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They also plan to further investigate the V-V dimer state in ilmenite-type MgVO3 using synchrotron X-ray experiments. “Our present study revealed the existence of the V-V dimer, but we haven’t yet clarified its electronic states,” Yamamoto concludes.
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