Pressure-Induced Structural Deformations in SeO2

The high-pressure behavior of low-dimensional selenium dioxide SeO2 (P42/mbc, Z=8) is studied with Raman scattering and synchrotron angle-dispersive X-ray powder diffraction in a diamond anvil cell up to 23 GPa at room temperature. Pressure-induced transformations in this material involve a sequence of structural distortions of the chain structure. The transformation occuring above 7.0 GPa is due to symmetry lowering to space group Pbam (Z=8) without major changes of the crystal lattice dimensions and coordination around the Se atoms. Like in the ambient pressure polymorph, the structural unit is a SeO3E polyhedron, where E is a Se non-bonded electron lone pair, or an irregular tetrahedron with the O atoms and Se lone pair at the vertices. Further structural transitions above 17 GPa are likely to be the result of additional distortions leading to monoclinic symmetry of the crystal structure. All transformations are reversible with little hysteresis.