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Abstract

The high-pressure behavior of low-dimensional selenium dioxide
SeO2 (P4(2)/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. (C) 2002
Elsevier Science (USA).