Publications Details

Compression behavior of dense H₂-He mixtures up to 160 GPa

Lim, Jinhyuk; Kim, Minseob; Duwal, Sakun D.; Ohishi, Yasuo; Hrubiak, Rostislav; Tse, John S.; Yoo, Choong-Shik

We have studied the compression behavior of H₂-He mixtures in comparison with pure H₂ and He using powder synchrotron x-ray diffraction and present the pressure-volume (PV) compression data of H₂-He mixtures to 160 GPa. The results indicate that both H₂ and He in H₂-He mixtures remain in hcp to the maximum pressure studied, yet develop a substantial level of lattice distortion in the (100) plane, most profound in He-rich solids and below 66 GPa. The measured PV data also indicate softening of He (or H₂)-rich lattice upon increasing the level of the guest H₂ (or He) concentration. We suggest that the observed softening and lattice distortion are due to a substitutional incorporation of H2 (guest) molecules into the basal plane of hcp-He (host) lattice and, thereby, reflect the miscibility between H₂ and He in H₂-He mixtures. Interestingly, solid He exhibits a lesser degree of preferred orientation in H2-He mixtures than in pure He, likely due to the presence of solid H₂ disturbing the crystalline ordering of He-rich solids. Finally, the present PV compression data of H₂-rich and He-rich solids to 160 GPa deviate from those of pure H₂ and pure He above ~70 and 45 GPa respectively, providing new constraints for development of the EOS for H₂-He mixtures for planetary models.