Facile precipitation of two phase alloys in SnTe0.75Se0.25 with improved power factor

• Observed metastable second phase that increases in mass fraction with low pressure.
• Improvement in electrical properties from presence of orthorhombic second phase.
• Concurrent application of heat and pressure stabilizes metastable second phase.
• Maximum power factor of 1.3 mW/m K2 at 494 K in SnTe0.75Se0.25.
• Best ZT of 0.19 achieved for SnTe0.75Se0.25, 3 times higher than peak ZT of SnTe.

Multiphase thermoelectric (TE) materials have received great interest in recent years due to the synergistic improvements in TE properties. We report for the first time on melt spun samples with nominal composition of SnTe0.75Se0.25. Interestingly, an orthorhombic second phase was observed to exhibit change in microstructure under low applied pressure – the metastable nature leads to an observed increase in mass fraction with increased applied pressure – and this second phase can be stabilized by concurrent application of heat and pressure during hot pressing. The second phase reduces electrical resistivity, while increasing Seebeck coefficient values slightly, especially at higher temperatures. A peak power factor of 1.3 mW/m K2 is obtained at 494 K, which is a 1.5 times enhancement over the peak power factor of pure SnTe. The peak ZT achieved for the alloy is 0.19 at 548 K, which is three times that of pure SnTe.