Optical characterization of LiIn5S8 single crystals

In previous studies the optical properties of the Li ternary compounds LiInS₂ and LiInSe₂ have been investigated in detail. The AB₅C₈ phase of most A^I - B^III - ternary systems with A = Cu, Ag is well known. The lattice vibrational properties of the sulfospinels CuIn₅S₈ and AgIn₅S₈ have been studied by several authors. In the system Li - In - S the LiIn₅S₈ phase also exists. In this work we report the lattice vibrational properties as well as the optical properties in the band gap region of LiIn₅S₈ for the first time. From the number of the Raman and infrared active lattice vibrational modes we have found that LiIn₅S₈ crystallizes in space group Fd3m (O_h ⁷). The band gap energy of LiIn₅S₈ was determined to be 2.29 eV at room temperature and 2.44 eV at 85 K.