Diamond at 800 GPa

A new compression technique, which enables the study of solids into the TPa regime, is described and used to ramp (or quasi-isentropically) compress diamond to a peak pressure of 1400 GPa. Diamond stress versus density data are reported to 800 GPa and suggest that the diamond phase is stable and has significant material strength up to at least this stress level. Data presented here are the highest ramp compression pressures by more than a factor of 5 and the highest-pressure solid equation-of-state data ever reported.

Figure 1

The inset shows a sketch of the target. Hohlraums had a diameter of 2 mm, a length of 2.24 mm, and a laser entrance hole diameter of 1.8 mm. The main figure shows incident laser intensity, characteristic temperature of the x-ray drive, and drive pressure on the diamond determined from the Lagrangian analysis.

Figure 2

(a) VISAR data record and analyzed velocity data for ramp-compressed diamond steps. (b) Pyrometer data with lineouts showing inferred temperatures. Different colors indicate data from different step thicknesses sketched in Fig. 1.

Figure 3

Lagrangian sound speeds versus particle velocity for 4 different experiments. The black curve is the weighted mean, and yellow and blue circles are the ambient-pressure longitudinal and bulk sound speeds, respectively [23, 24].

Figure 4

The main plot shows stress versus density for the weighted mean data in Fig. 3 (red line) compared with measured Hugoniot [28, 29, 30, 31, 32] and cold curve [24] data adjusted for the new ruby pressure scale [3]. The blue diamonds represent the original single-wave analysis, and the blue circles show the two-wave corrected analysis of Pavlovskii’s data as discussed in the text. The inset shows the deviatoric stress determined by comparing ramp compression data to the cold curve data (green circles) and a Vinet fit to the data (red line).