Journal of Physical Studies 7(3), 268–274 (2003) DOI: https://doi.org/10.30970/jps.07.268 THE SYMMETRY COORDINATES OF THE FUNDAMENTAL VIBRATIONS OF THE CRYSTAL Ag2CdI4 I. Bolesta1, O. Popel2, T. Kulay1 1Ivan Franko National University of Lviv, Department for Radiophysics 107 Tarnavskyj Str., Lviv UA–79000, Ukraine, 2ıt Ivan Franko National University of Lviv, Department for Theoretical Physics 12 Drahomanov Str., Lviv UA–79005, Ukraine

The compounds of the type $A_2BX_4$, in particular Ag$_2$CdI$_4$ belong to the crystals, whose structure and spectra are studied thoroughly. An interest in these materials is accounted for by the presence of the second order phase transition in the temperature region 360-400 K and also be the possibility of the existence of an incommensurate phase within the same temperature region. Therefore, the study of these systems is an important problem. The symmetric coordinates of the fundamental vibration are found. The analytical expressions for the frequencies and polarisation vectors of the fully symmetric vibrations are obtained.

PACS number(s): 05.20.$-$y, 03.30.+p

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