Figure 1

Integrated angle-dispersive powder diffraction profiles of Ga on pressure decrease from 16 GPa. $hkl$ indices are shown for Ga-III at 15.6 GPa. Arrows in the Ga-V and Ga-II profiles mark the position of $2k_F$ (see text). Inset (i) shows a Rietveld refinement fit of Ga-V to the $hR6$ structure at 12.2 GPa; some $hkl$ indices are given. Tick marks below the profile indicate peak positions of the $hR6$ structure. Below the tick marks is the difference between the observed and calculated profiles. Inset (ii) shows an expanded region of the Ga-II pattern at 3.0 GPa indexed on the $oC104$ unit cell with lattice parameters $a=5.966\AA$, $b=8.557\AA$, and $c=35.615\AA$. The notation $hk.l$ is used for $l\ge 10$.Reuse & Permissions

Figure 2

Crystal structures of Ga-II at 2.8 GPa, Ga-V at 12.2 GPa, and Cs-III at 4.3 GPa [7] shown on the same scale. The Ga-V structure and axes are viewed along a [101] direction to aid comparison with the hypothetical $cI12$ structure. The latter is shown with the same density as Ga-II, and corresponding volumes are marked in both of these structures. Cs-III and Ga-II are viewed along the $a$ axis of the $C{222}_1$ unit cell. The Ga-II cell origin is at $x=1/4$, $y=-1/8$ relative to the standard space group origin, to allow direct comparison. The 8- and 10-atom $a\mathrm{\text{−}}b$ layers in the two structures are numbered. Nonequivalent 8-atom layers are in two different shades of light gray. The 10-atom layers common to Ga-II and Cs-III are shown in black. The 10-atom layers 1 and 7, peculiar to Ga-II, are shown in dark gray. Contact distances up to 2.9 Å for Ga-V, 3.3 Å for Ga-II and $cI12$, and 4.7 Å for Cs-III are shown as solid lines.Reuse & Permissions

Figure 3

$a\mathrm{\text{−}}b$ layers of Ga-II and Cs-III viewed down the $c$ axis, and an 8-atom layer of Li-$cI16$ viewed along a $[110]$ direction (Ref. 9), are all shown the same size for clarity. Unit cells are marked by solid lines. Origins used and contact distances marked by solid lines are as in Fig. 2 for Ga-II and Cs-III. For Li, contact distances $<2.5\AA$ are shown. Dashed lines show longer nearest-neighbor distances in the range 3.3–3.6 Å (Ga-II) and 4.7–5.0 Å (Cs-III).Reuse & Permissions