Angle-Dispersive High-Pressure Synchrotron Radiation X-Ray Diffraction Studies of Pentaerythritol Tetranitrate on Compression Sequence up to 30 GPa

High-pressure synchrotron x-ray diffraction studies of pentaerythritol tetranitrate, C(CH$_{2}$ONO$_{2})_{4}$, have been performed \textit{in-situ} (diamond anvil cell). The spectral changes at low pressures (up to 7 GPa) indicated continuous densification of the tetragonal structure (space group $P\overline 4 2_{1}c)$ and the compound compressed with a 17{\%} decrease in the unit cell volume. At 8 GPa and above several new diffraction lines appeared in the patterns. These lines have been attributed to a pressure-induced structural transformation from the tetragonal to an orthorhombic structure (space group $P2_{1}22_{1})$. The progressive broadening of the diffraction lines that appeared with pressure increase beyond 10 GPa was attributed to a blend of two coexisting PETN phases with combined diffraction lines. More detailed high-pressure investigations will follow, in particular regarding the choice of the space group of the proposed new orthorhombic structure.