THE TlInS2–ZnS SYSTEM AND THE PROPERTIES OF THE TlInS2:Zn2+ CRYSTAL
Journal Title: Праці Наукового товариства ім. Шевченка - Year 2018, Vol 53, Issue
Abstract
Interactions of components in the TlInS2–ZnS systems were investigated by physico-chemical analysis methods. The system is of the eutectic type with limited mutual solid solubility of the starting components: L + (α and β are solid solution ranges of HT modification of TlInS2 and LT modification of ZnS, respectively). The eutectic point coordinates are 90 mol.% TlInS2 /10 mol.% ZnS and 997 K. The system features peritectoid processes of the phase transitions of TlInS2 and ZnS according to the reactions + at 886 K; L + at 1301 K. The solid solution range of TlInS2 extends to 5 mol.% ZnS at 670 K, while the solid solubility based on ZnS is less than 2.5 mol.% TlInS2. A TlInS2 single crystal doped with Zn was grown by the horizontal version og Bridgman-Stockbarger method with the starting composition 98 mol.% TlInS2 and 2 mol.% ZnS. The structure of the grown crystal was determined by X-ray powder method: monoclinic symmetry, space group C2/c. Spectral distribution of the absorption coefficient in the 100–300 K range was investigated, and bandgap energy for direct permitted transitions was estimated. The absorption coefficient in the energy region below the band edge is an exponential function of the photon energy which indicated the participation of the tails of the density of states in the formation of intrinsic optical transitions. Doping leads to some decrease of both direct and indirect bandgap energy compared to the original TlInS2 crystal (2.21–2.30 eV vs 2.28–2.55 eV). Such decrease of Eg may be explained by the mutually complementary processes upon the introduction of 2 mol.% ZnS to TlInS2, namely statistical substitution of In atoms by Zn atoms, and the increase of the concentration of thallium vacancies (VTl). We consider these processes as the dominating factors in the bandgap energy variations.
Authors and Affiliations
Lyudmyla PISKACH, Ganna MACHNOVETS, Galyna MYRONCHUK
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