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Recently, the experimental discovery of high-T c superconductivity in compressed hydrides H3S and LaH10 at megabar pressures has triggered searches for various superconducting superhydrides. It was experimentally observed that thorium superhydrides, ThH10 and ThH9, are stabilized at much lower pressures than LaH10. Based on first-principles density functional theory calculations, we reveal that the isolated Th frameworks of ThH10 and ThH9 have relatively more excess electrons in interstitial regions than the La framework of LaH10. Such interstitial excess electrons easily participate in the formation of the anionic H cage surrounding the metal atom. The resulting Coulomb attraction between cationic Th atoms and anionic H cages is estimated to be stronger than the corresponding one of LaH10, thereby giving rise to larger chemical precompressions in ThH10 and ThH9. Such a formation mechanism of H clathrates can also be applied to other superhydrides such as CeH9, PrH9, and NdH9. Our findings demonstrate that interstitial excess electrons in the isolated metal frameworks of high-pressure superhydrides play an important role in generating the chemical precompression of H clathrates.

The working principle and performance characteristics of a self-made oscillation tribo-tester were introduced. Under different oscillation frequency and pressure conditions, the friction coefficient and linear wear of spherical plain bearings with polytetrafluoroethylene (PTFE) woven liner were investigated. By using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), the wear mechanism of the spherical plain bearing was analyzed. The results indicate that with the oscillation frequency increases, the friction coefficient of spherical plain bearings decreased while the wear loss increased. In the high frequency of 4.8Hz, the reduction ranges of the friction coefficient is not obvious with the contact pressure increased, but the effect of contact pressure on the wear of the spherical plain bearing is great. During the experiment, adhesive wear, abrasive wear and spalling wear took place on the surfaces of woven liners.

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