Amplitudons and phasons in the triple-k incommensurate phase of quartz-type crystals
نویسندگان
چکیده
2014 The spectrum of amplitudons and phasons has been calculated for a 3-k triangular incommensurate structure (such as it is found in quartz-type crystals) using a phenomenological model. Two excitations have acoustic-like dispersion curves (gapless phasons) and four excitations are optic-like, one of the latter corresponding to fluctuations of the sum of the phases of the three modulation waves. The stability of the 3-k incommensurate structure with respect to these excitations is discussed and in particular a possible phason velocity softening is pointed out. The selection rules for infrared and Raman scattering activity of these excitations are derived. J. Physique 48 (1987) 1171-1179 JUILLET 1987, Classification Physics Abstracts 63.90 64.70K
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