Enhanced Thermoelectric Properties in the Counter-Doped SnTe System with Strained Endotaxial SrTe

We report enhanced thermoelectric performance in SnTe, where significantly improved electrical transport properties and reduced thermal conductivity were achieved simultaneously. The former was obtained from a larger hole Seebeck coefficient through Fermi level tuning by optimizing the carrier concentration with Ga, In, Bi, and Sb dopants, resulting in a power factor of 21 μW cm^-1 K^-2 and ZT of 0.9 at 823 K in Sn_0.97Bi_0.03Te. To reduce the lattice thermal conductivity without deteriorating the hole carrier mobility in Sn_0.97Bi_0.03Te, SrTe was chosen as the second phase to create strained endotaxial nanostructures as phonon scattering centers. As a result, the lattice thermal conductivity decreases strongly from ∼2.0 Wm^-1 K^-1 for Sn_0.97Bi_0.03Te to ∼1.2 Wm^-1 K^-1 as the SrTe content is increased from 0 to 5.0% at room temperature and from ∼1.1 to ∼0.70 Wm^-1 K^-1 at 823 K. For the Sn_0.97Bi_0.03Te-3% SrTe sample, this leads to a ZT of 1.2 at 823 K and a high average ZT (for SnTe) of 0.7 in the temperature range of 300-823 K, suggesting that SnTe is a robust candidate for medium-temperature thermoelectric applications.