Thermoelectric Properties Tuning in Mixed Valence Inorganic Solid Compound - In5S5Br by Oriented Mutual Chalcogenide Substitutions

The mixed-valence compounds In5S5Br, In5S3Se2Br, In5SSe4Br, and In5Se5Br reveal interesting thermoelectric properties. As the selenium content in the structure of In5S5Br increases, the Seebeck potential increases. In5S5Br exhibits low Seebeck potentials within the studied range (Delta T = 0-80 K) and a maximum value of 0.34 mV for AT = 80 K. It behaves as a p-type semiconductor. The substitution of two sulphur species by selenium, as in In5S3Se2Br, shows n-type conductivity and approx. -16.00 mV for the same Delta T. Further substitutions of sulphur in the structure maintain the n-type conductivity and increase dramatically the Seebeck potential to -225.26 mV (AT = 80 K). Repeating cycles of Seebeck potential variation over time for In5S5Br and In5SSe4Br, show differences in their potentials, shape of maxima as well as in their recovery time. Electrical conductivities from 0.3 pS for In5S5Br up to 13 pS for In5Se5Br, strongly influence their thermoelectricity.