Phonon Spectra and Phase Transitions in CuInP 2 (Se x S 1−x ) 6 and Sn 2 P 2 (Se x S 1−x ) 6 Ferroelectrics

On the Raman scattering data for mixed crystals Sn 2 P 2 (Se x S 1 m x ) 6 additional bands with intensity maximum lying at the center, or at the sulphide and selenide ends of the concentration interval are related to the internal vibrations of various anion impurity configurations. Intensity of additional bands is proportional to the probability of the appearance of structural P 2 (Se k S 6 m k ) (k = 0,…,6) groups with certain S and Se content for given solid solution concentration x and testifies the statistical distribution of chalcogen atoms in the solutions Sn 2 P 2 (Se x S 1 m x ) 6 . The concentration behavior of the Raman spectra for CuInP 2 (Se x S 1 m x ) 6 crystals has similar but more complicate character. This obviously is connected with more strong interaction between [P 2 S(Se) 6 ] 4 m anions inside the layers of layered crystals CuInP 2 S(Se) 6 comparatively with such interactions in case of Sn 2 P 2 S(Se) 6 crystals. By this could be explained strong smearing of the phase transitions in CuInP 2 (Se x S 1 m x ) 6 solid solutions comparatively with enough weak smearing of the ferroelectric transitions in Sn 2 P 2 (Se x S 1 m x ) 6 mixed crystals.

Keywords:

• thiophosphides
• selenophosphides
• ferroelectric Transitions
• vibration Spectrum