How do phasons differ from ordinary sound-wave vibrations in solids?

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quasicrystal Figure 1: Hexagonal lattice of atomic sites.

In quasicrystals, elastic deformations differ significantly from the standard vibrations found in ordinary solids. While ordinary sound waves, or phonons, involve standard displacements of atoms, phasons represent a unique second type of elastic deformation inherent to quasiperiodic structures.1

The primary differences include:

Nature of Deformation: Ordinary sound waves involve simple atomic displacements. In contrast, phasons correspond to rearrangements of relative atomic positions.1
Structural Adjustment: Eliminating a phason requires the adjustment of all atoms within a row of the quasicrystalline structure, a more complex process than the relaxation of standard acoustic waves.1
Temperature Dependence: At low temperatures, phason strain can become "frozen" into the material, which limits the perfection of the quasicrystal. At high temperatures near the melting point, phasons fluctuate continually as atoms jump between positions.1

While ordinary elastic response is measured via the speed of sound, phasons represent a distinct structural phenomenon arising from the translational quasiperiodicity of the material.1