Structural change in hBN coexisting with hydrogen gas under pressure

Hexagonal boron nitride (hBN) has the layered structure as graphite, while the magnitude of band gaps is very large ($\sim$0.59 eV). It is thought that hBN hardly causes charge transfer interaction with any atoms or molecules. On the other hand we examined pressure-induced structural-changes in multi-walled carbon-nanotubes (MWCNTs) and meso-carbon micro-beads (MCMBs) coexisting with hydrogen gas using a diamond anvil cell (DAC) at room temperature. Both of them showed abnormal pressure dependence of in-plane graphite-structure, suggesting intercalation of hydrogen. Then we thought hBN has also possibility to cause the intercalation of hydrogen using pressure. In this study x-ray diffraction of hBN coexisting with hydrogen was carried out at room temperature to investigate the pressure-induced intercalation of hydrogen from the point of view of structural study. Not only the interlayer distance but also the a-axis length show abnormal pressure dependence up to 1.5 GPa. In particular the a-axis length increases with increasing the pressure in the range between 1 and 1.5 GPa. According to the relatively-low quantitative-reproducibility of change, it is thought that the hBN-hydrogen system takes an un-steady and non-equilibrium state.