A B group monocrystals with chain-type crystal structure (TlSe, TIInSeZ, etc. ) /1/ occupy a special place in the row of compounds with strongly anisotropic crystal structure. They are perspective materials for optoelectronics /2/.The influence of hydrostatic pressure on the energy gaps of TlSe andTIInSeZ was investigated in /3 to 7/. The values of different authors for the pressure coefficients of indirect (dEi/dP) and direct (dE / d P ) energy gaps for TlSe and TlInSe2 a r e presented in Table 1. It is seen that these data a r e contradictory for TlSe.
The results of an experimental investigation of infrared reflection and Raman scattering spectra for TIS,Sel -, crystals are presented. The concentration dependence of infrared phonon frequencies on the composition of solid solutions is described by a modification of the isodisplacement model. The equations of motion in the model are written for a symmetrized displacement of the atoms. The results of the numerical estimations performed in the framework of this model are in good agreement with the experimental data on infrared reflection of TIS,Sel-, solid solutions (where 0 5 z 5 1). The values of the force constants and effective charges are derived from the best fitting of the estimated curves with those obtained experimentally. Die Ergebnisse einer experimentellen Untersuchung von Infrarot-und Raman-Streuspektren fur TISzSel -,-Kristalle werden mitgeteilt. Die Konzentrationsabhangigkeit der Infrarot-Phononenfrequenzen von der Zusammensetzung der Mischkristalle wird mit einer Modifikation des ,,Isodisplacement"-Modells beschrieben. Die Bewegungsgleichungen im Modell werden fur eine symmetrisierte Verschiebung der Atome aufgeschrieben. Die Ergebnisse der im Rahmen dieses Modells durchgefuhrten numerischen Rechnungen befinden sich in guter Ubereinstimmung mit den experimentellen Werten der Infrarotreflexion von TlS,Sel -,-Mischkristallen (wobei 0 5 z 5 1 ist).Die Werte fur die Kraftkonstanten und effektiven Ladungen werden aus der besten Anpassung der berechneten an die experimentellen Kurven abgeleitet.
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