Short-range order of compressed amorphous GeSe2.

L Properzi,F Baudelet,T Irifune,L Nataf,A Di Cicco

doi:10.1038/srep10188

Abstract

The structure of amorphous GeSe2 (a-GeSe2) has been studied by means of a combination of two-edges X-ray absorption spectroscopy (XAS) and angle-dispersive X-ray diffraction under pressures up to about 30 GPa. Multiple-edge XAS data-analysis of a-GeSe2 at ambient conditions allowed us to reconstruct and compare the first-neighbor distribution function with previous results obtained by neutron diffraction with isotopic substitution. GeSe2 is found to remain amorphous up to the highest pressures attained, and a reversible 1.5 eV red-shift of the Ge K-edge energy indicating metallization, occurs between 10 GPa and 15 GPa. Two compression stages are identified by XAS structure refinement. First, a decrease of the first-neighbor distances up to about 10 GPa, in the same pressure region of a previously observed breakdown of the intermediate-range order. Second, an increase of the Ge-Se distances, bond disorder, and of the coordination number. This stage is related to a reversible non-isostructural transition involving a gradual conversion from tetra- to octa-hedral geometry which is not yet fully completed at 30 GPa.

Highlights

The structure of amorphous GeSe2 (a-GeSe2) has been studied by means of a combination of twoedges X-ray absorption spectroscopy (XAS) and angle-dispersive X-ray diffraction under pressures up to about 30 GPa
Extended x-ray absorption fine structure (EXAFS) spectra of crystalline (c-GeSe2) and amorphous (a-GeSe2) germanium diselenide were analyzed by ab initio multiple-scattering calculations within a well established approach of EXAFS data analysis[16,17,18]
In the right-hand side panel of Fig. 4 we report the partial pair distributions resulting by present XAS data-analysis, showing that present refinement is in substantial agreement with ND results

Summary

Introduction

The structure of amorphous GeSe2 (a-GeSe2) has been studied by means of a combination of twoedges X-ray absorption spectroscopy (XAS) and angle-dispersive X-ray diffraction under pressures up to about 30 GPa. The properties of GeSe2 under high pressure have been studied in its liquid phase up to 5.1 GPa, evidencing the disruption of intermediate-range order by a reduction of the first-sharp diffraction peak (FSDP)[5] intensity. The interest for this substance is enhanced by the presence of a null-derivative point of the melting line around 1 GPa, which epitomizes the competition between two different packing conditions and which can be directly connected to the pressure-induced amorphization of its crystalline counterpart at room temperature[6]. The debate over the presence of a continuous rather than a broken bond network is still open[9]

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Conclusion