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Materials

Gallium declines to pick a phase

Researchers create gallium nanoparticles with solid cores and liquid shells

by Matt Davenport
August 1, 2016 | APPEARED IN VOLUME 94, ISSUE 31

Credit: Nat. Mater.
Energy-filtered transmission electron microscopy reveals the solid cores and liquid shells of gallium nanoparticles on a sapphire substrate.

Gallium has doubled down on its status as a quirky element by showing that it can support both liquid and solid phases simultaneously over a wide range of temperatures (Nat. Mater. 2016, DOI: 10.1038/nmat4705). Bulk gallium liquefies at 30 °C, the temperature of a warm summer’s day and a melting point much lower than most metals. Scientists led by April S. Brown of Duke University have discovered that gallium nanoparticles exhibit another thermal anomaly, existing as liquid blobs with solid cores from about –90 °C to 525 °C when the particles rest on rigid, inert sapphire substrates. Within the nanoparticle, the pressure is sufficiently high to crystallize the gallium near the core. Meanwhile, a balance between surface and interfacial forces creates an equilibrium that favors a liquefied shell. Although this balance stands up to large changes in temperature, it is upset by changing the chemical and mechanical properties of the substrate, the team shows. For instance, gallium particles formed a single liquid phase when deposited on reactive silicon substrates or on amorphous, deformable glass substrates. Selecting different substrates could give researchers a new dimension of control to tailor the properties of dual-phase nanoparticles for catalytic systems and optoelectronic devices.

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