Phonon-phason coupling in icosahedral quasicrystals

TL;DR

This study calculates the phonon-phason coupling constant in icosahedral quasicrystals using relaxation simulations, revealing small but potentially detectable effects that vary between different alloys.

Contribution

It provides the first microscopic calculation of phonon-phason coupling constants in quasicrystals, highlighting their sign and magnitude differences across alloys.

Findings

Coupling constant sign differs between alloys

Magnitude of coupling is about 1/10 of elastic constants

Criterion established for when effects are observable in diffraction patterns

Abstract

From relaxation simulations of decoration-based quasicrystal structure models using microscopically based interatomic pair potentials, we have calculated the (usually neglected) phonon-phason coupling constant. Its sign is opposite for the two alloys studied, i-AlMn and i-(Al,Cu)Li; a dimensionless measure of its magnitude relative to the phonon and phason elastic constants is of order 1/10, suggesting its effects are small but detectable. We also give a criterion for when phonon-phason effects are noticeable in diffuse tails of Bragg peaks.