Phase stability and electronic structure of iridium metal at the megabar range

V Monteseguro,G Garbarino,D Errandonea,W Olovsson,H Johan M Jönsson,S Pascarelli,T Irifune,F Cova,Igor A Abrikosov,V Cuartero,J A Sans,C Popescu

doi:10.1038/s41598-019-45401-x

Abstract

The 5d transition metals have attracted specific interest for high-pressure studies due to their extraordinary stability and intriguing electronic properties. In particular, iridium metal has been proposed to exhibit a recently discovered pressure-induced electronic transition, the so-called core-level crossing transition at the lowest pressure among all the 5d transition metals. Here, we report an experimental structural characterization of iridium by x-ray probes sensitive to both long- and short-range order in matter. Synchrotron-based powder x-ray diffraction results highlight a large stability range (up to 1.4 Mbar) of the low-pressure phase. The compressibility behaviour was characterized by an accurate determination of the pressure-volume equation of state, with a bulk modulus of 339(3) GPa and its derivative of 5.3(1). X-ray absorption spectroscopy, which probes the local structure and the empty density of electronic states above the Fermi level, was also utilized. The remarkable agreement observed between experimental and calculated spectra validates the reliability of theoretical predictions of the pressure dependence of the electronic structure of iridium in the studied interval of compressions.

Highlights

Iridium (Ir), with electronic structure [Kr]4d105s25p64f145d76s2, is one of the most incompressible 5d transition metals with face-centered cubic structure
It is important to underline that our experiments were carried out in quasi-hydrostatic conditions, so that the appearance of the mentioned reflections in the x-ray diffraction (XRD) patterns measured by Cerenius and Dubrovinsky could be due to the non-hydrostaticity of the pressure transmitting medium (PTM) used[12]
Ir metal has been studied by two complementary techniques, XRD and x-ray absorption (XAS), as well as by theoretical Density Functional Theory (DFT) calculations in order to characterize its high-pressure structure and electronic properties

Summary

Introduction

Iridium (Ir), with electronic structure [Kr]4d105s25p64f145d76s2, is one of the most incompressible 5d transition metals with face-centered cubic (fcc) structure. The study of the 5d metals under pressure have attracted the attention of the scientific community since the beginning of the 21st century because of the relevance of their behaviour under extreme conditions for improving the knowledge of planet interiors[6] In this sense, the debate on the structural stability of iridium under pressure has taken years. In 2000, Cerenius et al.[7] reported the formation of a complex superlattice in iridium above 59 GPa in a high-pressure energy-dispersive x-ray diffraction (XRD) experiment The structure of such a superlattice www.nature.com/scientificreports/. We clarify the structural stability, accurately determine the P-V equation of state (EoS) in the pressure range up to 1.4 Mbar, and report the high-pressure phase of Ir through a detailed quasi-hydrostatic XRD and x-ray absorption (XAS) study in which the effect of the pressure on the electronic structure of the Ir is explored. Besides obtaining careful information of the local structure of Ir, we attempt to use XAS to obtain information about the electronic and thermal effect of the CLC in this metal

Methods

Results

Conclusion