Renewable energy in focus: In5Se5Br, a solid material with promising thermoelectric properties for industrial applications

Abstract

We obtained via solid state synthesis needle-shaped crystals of In5Se5Br crystallizing in the space group Pmn21 and containing indium simultaneously in three different oxidation states: In+, formal In2+ and In3+. Bulk sample of In5Se5Br shows n-type conductivity and linear increase of Seebeck voltage with the temperature difference increase. Seebeck voltage of approx. 720mV is recorded at a temperature difference of 80K, corresponding to a Seebeck coefficient −8900μV/K. A voltage increase up to 250mV is recorded within 10min upon application of a 27K temperature difference between the contacts. On-off switching of the heating source unveils repeatable results. Linear I–U behavior with a resistivity of 2.32×1011Ω is observable for individual needles of In5Se5Br. In bulk In5Se5Br the resistivity oscillates between 2.6MΩ and 23MΩ. DTA and HT-powder XRD data show incongruent melting to InBr, InSe and In2Se3 at 805K. The ternary compound expands 1.02% along [010] showing a coefficient of thermal expansion αb=2.3(4)×10−5K−1. Lower expansions of 0.6% and 0.16% along a and c axes corresponding to mean coefficients of thermal expansion of αa¯=1.3(1)×10−5K−1, αc¯=4.4(5)×10−6K−1 are observed. Thin layer growing of In5Se5Br on glass substrate with targeted doping/substitutions can improve the sample conductivity, increase the Seebeck coefficient and lower the thermal conductivity making In5Se5Br a good alternative material for industrial thermoelectric applications.