Materials with layered structures XIII: electrical and optical properties of layered chalcogenides in the system CoIn_2S_4―CoIn_2Se_4

摘要

The system CoIn_2S_(4x)Se_(4(1-x)) has been investigated by X-ray powder methods on samples quenched at 700℃. The spinel type phase has a phase width of 1 ≥ x > 0.9. A new layered compound is formed for 0.9 > x > 0.45 which crystallizes with the α-FeGa_2S_4-type with a = 392.6 pm and c = 1270.3 pm (x = 0.5) for the hexagonal cell. Platelike crystals of the layered phase are obtained by transport reactions with iodine in a temperature gradient 750 → 700℃. The band gaps of these crystals measured by optical absorption vary from 1.2 to 1.4 eV. The electrical conductivities of the crystals are found in the order of 10~(-5) Ω~(-1) cm~(-1).