Tl2S-GeS-GeS2 system: Glass formation, macroscopic properties, and charge transport

Abstract

A relevant approach was found to study the glass-forming region, macroscopic properties and electrical conductivity changes in the Tl2S-GeS-GeS2 system by analysing two composition glass lines (Tl2S)x(GeS2)100-x (0 ≤ x ≤ 50) and (Tl2S)10(GeS)x(GeS2)90-x (0 ≤ x ≤ 90) together with three thallium containing crystalline compounds Tl4Ge4S10, Tl4Ge2S6 and Tl4GeS4. The crystallisation ability variation in the binary Tl2S-GeS2 system can be explained comparing the structural characteristics of glasses and closest crystalline compounds. The room temperature dc conductivity increases by 7 orders of magnitude with increasing thallium concentration and reaches the value of 10−8 S cm−1 for (Tl2S)50(GeS2)50 sample. Combined with the previously obtained conductivity and thallium diffusion parameters for (Tl2S)x(GeS)60(GeS2)40-x and (Tl2S)x(GeS)50-x/2(GeS2)50-x/2 composition lines as well as with conductivity characteristics for the crystalline analogues, the ionic and electronic conductivities in the (Tl2S)x(GeS2)100-x glasses were estimated separately. The Tl-poor glasses (x ≤ 0.25) are essentially semiconductors, while the Tl-rich vitreous alloys appear to be ionic conductors. The conductivity parameters for (Tl2S)10(GeS)x(GeS2)90-x glasses change non-monotonically with GeS concentration passing by the conductivity minimum for 60% mol. GeS. The same behaviour was observed for thallium free (GeS)x(GeS2)100-x matrix, showing the influence of the GeS/GeS2 ratio on the properties of the thallium-poor semiconducting glasses.