Lattice dynamical, electronic, and structural properties of complex metals at extreme conditions
Lead Research Organisation:
University of Edinburgh
Department Name: Sch of Physics and Astronomy
Abstract
I aim to exploit my expertise in optical and x-ray spectroscopy, x-raydiffraction, and first-principles computations to gain fundamental newinsight into the physical properties of complex elemental metals atextreme conditions in pressure and temperature. The research proposed hereconcerns the physics of elemental metals (such as Cs, Rb, Ba, Te) withcomplex crystal structures, where we have witnessed, in recent years, analmost revolutionary change in our understanding of the structural andbonding properties in elemental crystals under pressure. While there hasbeen as series of discoveries of remarkably and unexpectedly complexcrystal structures in elemental solids, very little is known about thephysical properties of these phases.I propose to make detailed studies of the lattice dynamical and electronicproperties of complex phases of elemental metals at extreme conditions inpressure and temperature. The experimental investigations will be based ona combination of spectroscopic techniques / optical Raman spectroscopy,inelastic x-ray scattering spectroscopy, as well as diffuse x-rayscattering analysis /, and will be closely coupled with computationalwork. X-ray diffraction investigations of structural aspects willcomplement the spectroscopic studies where needed. I will investigate thelattice dynamics of the remarkably complex and often incommensuratestructures that have been found in K, Rb, Sr, Ba, Sc, As, Sb, Bi, S, Se,Te and Ga at high pressures. In addition to studies of phonon softeningand other anomalies in their phonon dispersion curves, I will embark on anambitious programme of studies on their electronic properties. I willinvestigate the superconducting gap in superconducting phases to gainunderstanding of the pairing mechanism, and aspire to detect andcharacterise pseudogaps in the electronic excitation spectra. Altogether,this research aims at gaining fundamental new insight in the behaviour andproperties of elemental metals at high pressure and at developing acoherent picture of the mechanisms that lead to the unexpectedly frequentformation of complex crystal structures under pressure.
Organisations
People |
ORCID iD |
| Ingo Loa (Principal Investigator) |
Publications
Evans S
(2009)
Phase transitions in praseodymium up to 23 GPa: An x-ray powder diffraction study
in Physical Review B
Husband R
(2012)
The Structure of Eu-III
in Journal of Physics: Conference Series
Husband R
(2013)
Phase transitions in europium at high pressures
in High Pressure Research
Husband R
(2014)
The distorted-fcc phase of samarium
in Journal of Physics: Conference Series
Husband R
(2014)
Incommensurate-to-incommensurate phase transition in Eu metal at high pressures
in Physical Review B
Husband RJ
(2012)
Europium-IV: an incommensurately modulated crystal structure in the lanthanides.
in Physical review letters
Loa I
(2012)
Lattice dynamics and superconductivity in cerium at high pressure.
in Physical review letters
Loa I
(2009)
Origin of the incommensurate modulation in Te-III and fermi-surface nesting in a simple metal.
in Physical review letters
Loa I
(2012)
Extraordinarily complex crystal structure with mesoscopic patterning in barium at high pressure.
in Nature materials
Lundegaard L
(2009)
Single-crystal studies of incommensurate Na to 1.5 Mbar
in Physical Review B
| Description | The main scientific aims of the project were to explore the properties of unusual high-pressure phases of elemental metals with complex crystal structures and to gain a fundamental understanding of the mechanisms that lead to their formation. On the scientific side, the use of inelastic x-ray scattering (IXS) to study the lattice dynamics in solids at high pressure has been significantly advanced during the fellowship. Tellurium, cerium, zirconium, rubidium and barium have been studied in detail in IXS experiments, performed at the European Synchrotron Radiation Facility in Grenoble (France). In tellurium at 8 GPa, pronounced lattice dynamical anomalies were discovered experimentally and reproduced subsequently in electronic structure and lattice dynamical calculations. These calculations then allowed me to identify unexpectedly efficient Fermi surface nesting and strong electronic-phonon coupling as the origin of the incommensurately-modulated structure of tellurium at high pressure, and the same mechanism appears to be relevant for selenium and sulphur. In a high-pressure phase of cerium at ~6 GPa, phonon anomalies were also discovered, and they are surprisingly similar to those of isostructural uranium at ambient pressure, given that the two elements have very different electronic configurations. Complementary electronic structure calculations provided insight in the high-pressure superconductivity of this element and also indicated that cerium may adopt a charge-density wave-state at around 4 GPa and low temperatures, which, if confirmed experimentally, would add another facet to the unusual properties of this element. Significant progress has been made in using thermal diffuse scattering of x-rays for determining the lattice dynamical properties in elemental phases. Experiments have been performed successfully on three different phases of cesium at high pressure, and the development of the data analysis software is in progress. Important advances have also been made with regards to synchrotron-based single-crystal x-ray diffraction experiments of materials at extreme conditions of pressure and temperature. Highlights in this area are firstly the discovery of the first phase with an incommensurately-modulated crystal structure in the lanthanide elements, europium-IV, and secondly what I consider to be the most complex crystal structure now known to exist in the pure elements. It is the structure of a high-pressure phase of barium at around 19 GPa which gives beautiful x-ray diffraction patterns of intricate detail. It is a host-guest structure with a basic unit containing 768 atoms (in contrast to up to four in the "normal" structures of elemental metals), where the relative alignment of the guest chains can be represented by a pattern of intertwined S-shaped units. And complementary electronic structure calculations and an analysis based on pseudopotential theory have uncovered the electronic origin of such unusual crystal structures. Overall, the project has achieved many technical and scientific advances. |
| Exploitation Route | The scientific findings as published in a series of articles in scientific journals have influenced and inspired further research as judged by more than 80 citations in scientific articles by other researchers. |
| Sectors | Other |
| Description | The scientific publications resulting from the fellowship have been recognised in the international research community as judged by over 80 citations by other authors. A central result of this research regarding the extraordinarily complex crystal structures in the element barium at high pressure is now regularly presented by keynote speakers as a highlight in physics under extreme conditions. |
| Sector | Other |