Infrared Studies of the Layered Compound ZnIn2S4

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Abstract
Infrared transmission and reflectance measurements are made on single crystals of the layered compound ZnIn2S4 with C3v5 structure in the range between 4000 and 33 cm‐1,. According to group‐theoretical analysis there are altogether 4A1 + 6E zone centre optical modes which are both ir‐ and Raman‐active. 4A1 + 4E modes should be intralayer modes, the remaining 2A1 + 2E ones should be rigid layer modes with distinctly lower frequencies. The number of observed one‐phonon frequencies is found to be by far larger than expected. 16 frequencies of ZnIn2S4 are found to coincide very well with frequencies of certain critical‐point phonons of cubic ZnS and with certain phonon frequencies of β‐In2S4 respectively. The “additional” frequencies related to the number of frequencies predicted by group theory, which occur in the ir spectrum, are believed to arise from broken translational symmetry of the lattice.