Polytypes of monoclinic TlInS2

The polytypes of monoclinic TlInS 2 ( c ∼ 15, 60, 120 Å) and triclinic TlInS 2 ( c ∼ 30 Å) were prepared. The positions of edge excitons and the band gaps were determined by the optical and photoelectric measurements. It was found that the maxima in the temperature dependences of dielectric constants of pure polytypes are situated at different temperatures. The photoconductivity spectra and the capacitive measurements showed that pure polytypes are unstable and transform with time into a mixture of the monoclinic polytypes of TlInS 2 . It is also established that all polytypes of monoclinic crystals tend to transform to the triclinic system.