High-pressure melting curve of helium and neon: Deviations from corresponding states theory

The melting curves of He and Ne were measured up to 80 and 70 GPa, respectively, significantly extending the pressure range of previous measurements. Melting was detected in situ by the laser speckle method using the laser-heated diamond-anvil cell. Temperatures were measured in the visible as well as infrared range. Our He melting curve differs considerably from earlier experimental data above 30 GPa. The present Ne melting curve does not agree with the predictions from corresponding states theory in the range from 15 to 70 GPa.

Figure 1

Schematics of the experimental setup used for the melting studies of He and Ne. The flip mirror M1 is used to observe the laser speckle using an argon laser (488 nm). For temperature measurement using spectrometer 1 with PIXIS 100B CCD, M1 is removed. For measurements using Spectrometer 2 with InGaAs CCD, AM2, and M2 are moved away.

Figure 2

Melting curve of He. The present data is represented by (a) filled squares (taken with InGaAs CCD in the infrared range); (b) filled circles (taken with PIXIS 100B CCD in the visible range). Previous experimental data are represented by (a) triangles (Refs. 9, 11), (b) open circles (Ref. 17), and (c) stars (Ref. 19). Dotted and dashed lines represent the fittings to the Simon-Glatzel equation reported by Vos et al. (Ref. 17) and the Kechin equation reported by Datchi et al. (Ref. 19), respectively. Kechin equation fit to the present data is represented as a solid line. The theoretical melting points reported by (a) Loubeyre and Hansen (Ref. 14) are given by crosses and (b) Koči et al. (Ref. 20) given by pentagons.

Figure 3

Melting curve of neon. The open symbols belong to melting data points using W absorbers of different thickness: (a) open squares represent thickness of about 8 micron; (b) open circles represent thickness of about 4–6 micron; (c) open stars represent thickness of about $6–8\mu \text{m}$. Filled pentagons are data points obtained using diamond heaters and filled triangles represent loosely packed Ir black absorbers. The low pressure melting data represented by filled squares are taken from Vos et al. (Ref. 24).

Figure 4

Dotted, dashed, dot-dash and solid lines represent the predicted melting curves of Ne, Ar, Kr, and Xe obtained by corresponding states scaling from our He melting curve. To compare, the solid points corresponding to experimental melting data: filled stars (Ref. 24) and open stars (present work) for Ne; filled triangles (Ref. 33) and open triangles (Ref. 5) for Ar, filled circles for Kr (Ref. 5) and open squares (Ref. 5) and filled squares (Ref. 34) for Xe.