Crystal structure and lattice dynamics of AlB2 under pressure and implications for MgB2

TL;DR

This study investigates how high pressure affects the crystal structure and lattice vibrations of AlB2, revealing no phase transition up to 40 GPa and exploring implications for the superconducting properties of MgB2.

Contribution

It provides the first detailed analysis of AlB2 under pressure using experimental and computational methods, highlighting the role of non-stoichiometry in phonon behavior and superconductivity.

Findings

No pressure-induced structural phase transition up to 40 GPa

Al deficiency affects electronic structure and phonon pressure dependence

Possible explanation for variability in MgB2's critical temperature

Abstract

The effect of high pressures to 40 GPa on the crystal structure and lattice dynamics of AlB2 was studied by synchrotron x-ray powder diffraction, Raman spectroscopy, and first-principles calculations. There are no indications for a pressure-induced structural phase transition. The Raman spectra of the metallic sample exhibit a well-defined peak near 980 cm^{-1} at 0 GPa which can be attributed to the Raman-active E_{2g} zone-center phonon. Al deficiency of ~11% in AlB2, as indicated by the x-ray data, changes qualitatively the electronic structure, and there are indications that it may have a sizable effect on the pressure dependence of the E_{2g} phonon frequency. Similar changes of the pressure dependence of phonon frequencies, caused by non-stoichiometry, are proposed as an explanation for the unusually large variation of the pressure dependence of T_c for different samples of MgB2.