Incommensurate modulated structure
From Online Dictionary of Crystallography
Structure modulée incommensurable (Fr.)
An incommensurate modulated crystal structure is a modulated crystal structure, for which the modulation function has a Fourier transform of sharp peaks at wave vectors that cannot all be expressed by rational coefficients in a basis of the reciprocal lattice of the basic structure. At least one of the components of the wave vectors of the modulation with respect to the basis structure should be irrational.