Experimental compressions for normal hydrogen and normal deuterium to 25 kbar at 4.2 K

Abstract

The piston-displacement technique has been used to determine the pressure-volume relations for normal hydrogen ($n-{\mathrm{H}}_2$) and normal deuterium ($n-{\mathrm{D}}_2$) at pressures to 25 kbar at 4.2 K. The accuracy of the relative compressions $\frac{V}{V_0}$ ranges from ±${10}^{-3\mathrm{}}$ at low pressures to ±3×${10}^{-3\mathrm{}}$ at 25 kbar. The data, especially for $n-{\mathrm{H}}_2$, agree well with earlier 20-kbar results, and the extrapolated $P=0\mathrm{}$ bulk moduli, 1.70 ± 0.06 kbar for $n-{\mathrm{H}}_2$ and 3.15 ± 0.06 kbar for $n-{\mathrm{D}}_2$, are consistent with recent ultrasonic data. The shapes of the pressure-volume relations resemble more closely those for the helium isotopes than those for the heavier-rare-gas solids, and suggest that the two-body repulsive interaction for hydrogen molecules (and helium atoms) varies more slowly with intermolecular spacing than that for the heavier-rare-gas atoms. These experiments also give maximum values for the pressure-dependent shear yield stress of solid hydrogen.