Raman spectra of CuInTe2, CuIn3Te5, and CuIn5Te8 ternary compounds

From the analysis of Raman spectra, a comparative study of the lattice vibr ational modes in CuInTe2, and of the ordered defect compounds (ODC) CuIn3Te 5 and CuIn5Te8 of the Cu-In-Te system is reported. It is found that Raman l ines in the ODCs appear at very nearly the same frequency as in CuInTe2. Th is is explained on the basis that the cation vacancy should not be consider ed merely as an empty site in the lattice but a localized region of positiv e Coulomb potential that attracts the valence electrons of the surrounding anions. It is proposed that the vacancy-Te force constant caused by the pos itive potential is of the same magnitude as in the Cu-Te stretching bond. T he symmetry assignment of the observed lines is tentatively made by a compa rative study of the vibrational modes of its binary analog Zn0.5Cd0.5Te, wi th phonon modes observed in CuInTe2 from polarized infrared optical measure ments, and by estimating the modes frequency using several models reported in the literature for the chalcopyrite compounds. These are A(1) mode at 12 7 cm(-1); B-1 at 58, 114, and 146 cm(-1), E modes at around 48, 72, 137, 16 0, 192, and 218 cm(-1); B-2 at 64 and 104 cm(-1); and E and/or B-2 at 170 a nd 184 cm(-1). The highest phonon frequencies observed at 237 and 270 cm(-1 ) are attributed to the combination of E and B-2 modes. (C) 2000 American I nstitute of Physics. [S0021-8979(00)03419-8].