Figure 1

(a) Diffraction images from liquid and solid phases of Na, collected at 5.8 GPa using synchrotron radiation with wavelength $\lambda =0.3888\AA$, and at 123 and 124 GPa using $\lambda =0.4233\AA$. The $hkl$ indexing for the bcc diffraction peaks of Na is shown. The peaks of sodium at 123 GPa are marked by “Na”; the spots on the diffraction rings originating from tantalum are marked by “Ta”. All diffraction peaks in the 124 GPa image originate from the Na sample. (b) Diffraction patterns from liquid and solid phases of Na at 5.8 GPa, 123 GPa, and 124 GPa, obtained from the integration of the images shown on the left. The diffraction peaks from bcc Na, hcp Re, and bcc Ta are indexed.Reuse & Permissions

Figure 2

(a) Diffraction patterns of liquid Na with subtracted background, obtained from different sample loadings at different pressures immediately after melting. The data for liquid Na at ambient pressure are from Ref. 41 and the diffraction pattern of ambient pressure bcc Na is given for comparison. The peaks marked with “Re” are from gasket material; the peak marked "Ta" is from tantalum. (b) pressure dependence of $Q$ of the first diffraction peak of liquid Na (solid symbols) and the 110 diffraction peak of bcc Na (open symbols). The solid lines show the equation of state taken from [8], and the dashed line is a guide to the eye.Reuse & Permissions

Figure 3

The melting curve of Na to 130 GPa. The filled symbols are from the present work with different symbols corresponding to the melting of different Na phases. The open squares are from Ref. 10. The solid line gives the melting curve of bcc Na obtained using the Kechin equation between ambient pressure and 65 GPa; above 65 GPa the solid line is a guide for the eye only (see text). Dashed lines show tentative phase boundaries. The phase relations in the vicinity of the fcc-bcc-liquid triple point are notional. Arrows show various $P$-$T$ paths followed in the experiments (small pressure shifts on heating are not shown). The inset shows the melting curve of Na (present work) in comparison with the melting curves of ${\mathrm{H}}_2$ (Ref. 19) and He (Ref. 30) and K (Ref. 10).Reuse & Permissions