Thermoelectric performance of n-type Bi₂S₃-alloyed Bi₂Te_2.7Se_0.3

The effect of isovalent sulfur substitution on the thermoelectric properties of n-type Bi₂Te_2.7Se_0.3 alloy has been studied systematically. At low sulfur concentrations, where the samples are single phase, changes in defect chemistry and density of states impacted significantly electrical resistivity and thermopower. Isovalent sulfur substitution enhanced thermopower and reduced thermal conductivity for both single and multiphase samples. This reduction in thermal conductivity was particularly noticeable in samples containing Bi₂S₃-based secondary phase, reaching a low thermal conductivity of ∼0.3 W m⁻¹ K⁻¹ at 525 K. A maximum figure of merit, zT, of 0.55 was achieved for the sample with the highest sulfur content, demonstrating the potential of this approach to optimise the thermoelectric performance of Bi₂Te₃-based materials.