Full-multiple-scattering calculations on HgTe under high pressure at the mercury L-2,L-3 x-ray-absorption edges

Full-multiple-scattering (FMS) calculations have been performed to reproduce the modifications observed on the mercury L-3 edge in the x-ray-absorption near-edge structure (XANES) spectra of the II-VI HgTe compound under increasing pressure. HgTe undergoes several structural phase transitions with pressure, i.e., zinc blende (phase I)--> cinnabar (phase Il)--> rocksalt (phase III)--> unknown structure (phase IV). The best FMS simulations are obtained for the relaxed and screened final-state potential with a complex Dirac-Hara exchange potential with muffin-tin symmetry and nonoverlapping spheres. They reproduce satisfactorily the main edge changes occurring during the first two phase transitions. At P=12 GPa, HgTe undergoes a third transition (phase IV) to an orthorhombic structure. The resolution of this high-pressure structure is controversial. Confident in the ability of FMS calculations to well reproduce the XANES modifications, we used this formalism to choose between structures in competition for phase IV. Calculations have been performed considering successively the three different structural models proposed for phase IV: a P-Sn-like structure and two orthorhombic structures with space group Cmcm, labeled Cmcm(1) and Cmcm(2), respectively. The trends observed on the XANES spectra during the rocksalt --> phase IV transition are satisfactorily reproduced by two of the three models, Cmcm(2) being totally refuted. Although the differences between the calculations based on the two acceptable models are not great, the orthorhombic structure Cmcm(1) gives a slightly better agreement than the beta-tin structure.