Possible superlattice formation in high-temperature treated carbonaceous MgB2 at elevated pressure

TL;DR

This study investigates a phase transition in carbonaceous MgB2 under high pressure and temperature, revealing structural changes and potential superlattice formation through spectroscopic and diffraction techniques.

Contribution

It provides evidence of a pressure-induced structural transition in MgB2, suggesting possible superlattice formation and changes in electron-phonon interactions.

Findings

Indications of a second-order structural transition above 9 GPa

Doubling of the unit cell along c-axis observed

Reduction in electron-phonon coupling inferred

Abstract

We report indications of a phase transition in carbonaceous MgB2 above 9 GPa at 300 K after stress relaxation by laser heating. The transition was detected using Raman spectroscopy and X-ray diffraction. The observed changes are consistent with a second-order structural transition involving a doubling of the unit cell along c and a reduction of the boron site symmetry. Moreover, the Raman spectra suggest a reduction in electron-phonon coupling in the slightly modified MgB2 structure consistent with the previously proposed topological transition in MgB2. However, further attributes including deviatoric stress, lattice defects, and compositional variation may play an important role in the observed phenomena.