Pressure-Induced Decomposition of Hydrogen Peroxide

We have studied the pressure-induced chemical decomposition of pure ($\sim $97.5{\%}) hydrogen peroxide to 50 GPa, using confocal micro-Raman and synchrotron X-ray diffraction. Our results indicate that pure hydrogen peroxide crystallizes into a tetragonal structure (P4$_{1}$2$_{1}$2), the same structure of 90 {\%} H$_{2}$O$_{2}$ previously reported below 8 GPa and of pure H$_{2}$O$_{2}$ at low temperatures. The tetragonal phase (H$_{2}$O$_{2}$-I) is stable to 15 GPa, above which transforms into an orthorhombic structure (H$_{2}$O$_{2}$-II) over a large pressure range between 15 and 20 GPa. The diffraction pattern of H$_{2}$O$_{2}$-II is analogous to that of $\varepsilon $-oxygen, suggesting a similar packing of oxygen atoms between H$_{2}$O$_{2}$-II and $\varepsilon $-O$_{2}$. In fact, we found that H$_{2}$O$_{2}$-II eventually decomposes to into H$_{2}$O and O$_{2}$ at 45 GPa.