Raman Scattering of Metals to Very High Pressures

TL;DR

This paper reviews advanced Raman spectroscopy techniques and diamond anvil cell technology enabling high-pressure measurements of metals, revealing insights into their structural and electronic properties under extreme conditions.

Contribution

It introduces improved Raman measurement methods for metals at megabar pressures, including new optical setups and diamond quality improvements, expanding high-pressure metal studies.

Findings

Observation of Raman peaks in metals at very high pressures

Determination of phonon mode shifts and Grüneisen parameters

Insights into structural and electronic transitions under pressure

Abstract

We review recent development in Raman techniques and diamond anvil cell technology, that allow measurements of Raman of metals in the megabar pressure range. The Raman technique includes holographic transmission optics and single-stage spectrographs with CCD array detectors. Use of synthetic high-purity diamonds and anglular excitation geometry reduces spurious background scattering substantially, which makes observable very weak Raman peaks in metals. We give several examples of studies including the hexagonal close packed (hcp) $\epsilon$-Fe, Fe$_{(1-x)}$Ni${_x}$, and Re and the recently discovered high-temperature superconductor MgB$_2$. The shift of phonon modes with pressure is used for determination of the mode-Gr\"uneisen parameters, estimation of shear elastic moduli and provide information on structural and electronic transitions.