High-Pressure Modification of BiI3

Ulrich Schwarz,Alim Ormeci,Lev Akselrud,Aron Wosylus,Volker Hermann,Christine Kuntscher,Michael Hanfland,Marcus Schmidt

doi:10.3390/inorganics7120143

Ulrich Schwarz, Alim Ormeci + Show 6 more

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https://doi.org/10.3390/inorganics7120143

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Abstract

Structural and optical properties as well as chemical bonding of BiI3 at elevated pressures are investigated by means of refinements of X-ray powder diffraction data, measurements of the optical absorption, and calculations of the band structure involving bonding analysis in real space. The data evidence the onset of a phase transition from trigonal (hR24) BiI3 into PuBr3-type (oS16) BiI3 around 4.6 GPa. This high-pressure modification remains stable up to 40 GPa, the highest pressure of this study. The phase exhibits semiconducting properties with constantly decreasing band gap between 5 and 18 GPa. Above this pressure, the absorbance edge broadens significantly. Extrapolation of the determined band gap values implies a semiconductor to metal transition at approximately 35 GPa. The value is in accordance with subtle structural anomalies and the results of band structure calculations. Topological analysis of the computed electron density and the electron-localizability indicator reveal fingerprints for weak covalent Bi-I contributions in addition to dominating ionic interactions for both modifications.

Highlights

In the context of current studies of materials with large spin-orbit coupling as topological materials [1,2], compounds of heavy elements attract widespread interest
Bismuth compounds and especially halides are in special focus as their atomic arrangements often exhibit low-symmetry patterns caused by the stereochemical activity of lone pairs [3,4,5,6]
The reflection reflection positions can be indexed using an orthorhombic unit cell, and the the crystal crystal structure structure solution of the the high-pressure high-pressure modification is in accordance with an atomic arrangement of the PuBr33-type

Summary

Introduction

In the context of current studies of materials with large spin-orbit coupling as topological materials [1,2], compounds of heavy elements attract widespread interest. Bismuth compounds and especially halides are in special focus as their atomic arrangements often exhibit low-symmetry patterns caused by the stereochemical activity of lone pairs [3,4,5,6]. Their structural and physical properties can be substantially modified by application of hydrostatic pressure [7,8,9,10]. Displacement of the metal atoms with respect to the center of the octahedra is attributed to the stereochemical activity of lone pairs located on the bismuth atoms. The high-pressure structure of BiI3 was assigned to the monoclinic structure type of SbI3 , but the diffraction data were measured without using a pressure-transmitting medium

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Discussion

Conclusion