Existence of Partially Degenerate Electrical Transport in Intermetallic Cu₂SnSe₃ Thermoelectric System Sintered at Different Temperatures

A detailed investigation on the temperature dependent electrical properties of Cu₂SnSe₃ system, synthesized via conventional solid-state reaction at different sintering temperatures are presented in this communication. All the samples exhibit degenerate semiconducting nature at low temperatures. The existence of small polarons and hence electron–phonon interactions are confirmed at temperatures below 400 K. A transition was observed from degenerate to non-degenerate semiconducting behaviour at high temperatures (T > 400 K). The study confirms the unusual transition in electrical resistivity as well as thermopower at high temperatures in all the compounds, demonstrating the existence of minority carrier excitation along with temperature-triggered ionisation of the defects. The transport behaviour is further supported by an upward movement of Fermi level away from the valence band. Highest weighted mobility of 8.2 cm² V⁻¹ s⁻¹ at 673 K was obtained for the sample sintered at 1073 K. A considerable decrease in electrical resistivity with increase in temperature (T > 400 K) has driven the power factor to increase exponentially, thereby achieving highest value of 188 µV/mK² (at 673 K) for the sample sintered at 673 K. Graphic abstract: [Figure not available: see fulltext.]