Unusual Freezing and Melting of Gallium Encapsulated in Carbon Nanotubes

The freezing and melting behavior of gallium (Ga) encapsulated in carbon nanotubes was investigated through in situ observation in a transmission electron microscope. It is shown that Ga remains liquid up to $\ensuremath{-}80\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ when encapsulated in carbon nanotubes. Results of detailed electron diffraction analysis show that the encapsulated Ga can crystallize in either $\ensuremath{\beta}$ phase or $\ensuremath{\gamma}$ phase rather than the common $\ensuremath{\alpha}$ phase upon freezing. Both $\ensuremath{\beta}$-Ga and $\ensuremath{\gamma}$-Ga melt at around $\ensuremath{-}20\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. While this is very close to the melting point of bulk $\ensuremath{\beta}$-Ga ($\ensuremath{-}16\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$), it is considerably higher than that of bulk $\ensuremath{\gamma}$-Ga ($\ensuremath{-}35.6\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$). It was observed that upon solidification, Ga has its unique crystallographic orientation relative to the host carbon nanotube.