What is "phason"

n. (context physics English) A quasiparticle existing in quasicrystals due to their specific, quasiperiodic lattice structure.

Phason is a quasiparticle existing in quasicrystals due to their specific, quasiperiodic lattice structure. Similar to phonon, phason is associated with atomic motion. However, whereas phonons are related to translation of atoms, phasons are associated with atomic rearrangements. As a result of these rearrangements, waves, describing the position of atoms in crystal, change phase, thus the term "phason".

The hydrodynamic theory of the quasicrystals predicts that the conventional (phonon) strain relaxes rapidly. On the contrary, relaxation of the phason strain is diffusive and is much slower. Therefore, metastable quasicrystals grown by rapid quenching from the melt exhibit built-in phason strain associated with shifts and broadenings of X-ray and electron diffraction peaks.