POLAR VIBRATIONAL-MODES IN AG3ASS3 CRYSTALS

Reflectivity spectra of Ag3AsS3 crystals have been investigated in the range from 50 to 4000 cm(-1) for E parallel to c and E perpendicular to c polarizations, and practically all expected vibrational modes of A(1) and E symmetry have been found. Phonon parameters, i.e. frequenci es of LO and TO modes, longitudinal-transverse splitting and deilectri c constants epsilon(infinity) and epsilon(0) are determined. Effective ionic charges of Ag, As and S ions and their anisotropy are estimated .