A great number of bands have been observed by light scattering and infrared absorption in Cu,O crystals corresponding to transitions most of which are normally forbidden in the perfect crystal. An analysis of the symmetry properties of the lattice modes in the presence of defects is given. I n particular the role of each symmetry site for the defects is investigated and the observed modes interpreted as being due to activated band modes and localized modes. Double phonon processes are observed as well as the normally allowed optical transitions for the perfect crystal.Un grand nombre de bandes sont observbes par diffusion de la lumibre et absorption infrarouge dans d u Cu,O correspondant t i des transitions pour la plupart interdites dans le cristal parfait. Une analyse des propribtbs de symktrie des modes du rbseau en presence de dkfauts est donnbe. E n particulier le role de chaque site de symktrie pour le d6faut est Btudie et les modes observes sont interpret& comme &ant diis h des modes de bande actives par les dkfauts ou a des modes localisks. Des processus A deux phonons sont observes aussi bien que les transitions normalement permises pour le cristal parfait.
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