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The far infrared spectra are investigated of cubic wIn,S, and tetragonal P-In,S, for E _L c and E I I e configurations for samples obtained after quenching and also after a long period of annealing.The quenched samples show a high reflectivity in the low frequency range, which disappears after annealing. Also for ci-In,S, a greater number of bands appears after annealing. A large number of' peaks are also observed in light scattering, which are concentrated in the same narrow frequency range, as in the infrared spectra.Nous avons examine les spectres infrarouge lointain d'echantillons de a-In,S, cubique et de p-In,S, tetragonal dans des configurations E I c and E 11 c. Deux types d'hchantillons ont 6th BtudiBs:des Bchantillons trempBs et des Bchantillons recuits sur de longues phriodes. Les Bchantillons trempes montrent une forte rBflectivit6 L basse frhquence, qui disparait aprks recuit. Pour cc-In&, le nombre de bandes observBes augmente a p r h recnit. Un grand nombre de pics sont observbs aussi par diffusion de la lumiitre qui correspondent h des excitations situBes dans la mdme bande, Btroite, de frequence que celles observees en infrarouge lointain.

The supcrst,ructures of tantalum and niobium pentoxide a.re studied. The observations made support the aasumption that these, and related crystals, have a "shear structure" and that this shear structure can be observed directly. It is shown that the size of the unit cell depends on the exact stoichiometry of the compound. A model is proposed which explains both the details of the diffraction pattern and the geometry of the line system. Es werden die Superstrukturen von Tantal-und Niobiurnpentoxyd untersucht. Die gemachten Beobachtungen fuhren zii der Annahme, daB diese nnd iihnliche Kristalle eine ,,Scherungsstruktur" haben, und daI3 dicse Scherungsstruktur direkt beobachtet werden kann. Es wird gezeigt, daI3 die Grone dcr Einheitszelle von der exakten Stochiometrie der Verbindung abhangt. Ein Modell wird vorgeschlagen, das die Einzelheiten des Beugungsbildcs und die Geometric des Liniensystems erklSrt.