Enhancing the average thermoelectric figure of merit of elemental Te by suppressing grain boundary scattering

P-type elemental Te has exhibited a high thermoelectric (TE) figure of merit zT of similar to 1.0 around 600 K, but its performance near room temperature is much deteriorated due to grain boundary scattering. In this work, the average zT of Te0.98As0.02 alloys is remarkably enhanced via increasing the grain size. Through increasing the grain size, the room temperature power factor is boosted from 0.44 x 10(-3) W m(-1) K-2 to 1.2 x 10(-3) W m(-1) K-2 due to the suppression of grain boundary scattering, while the lattice thermal conductivity remains unchanged, resulting in an similar to 32% enhancement of device zT. The TE performance is further enhanced via Se alloying to reduce the lattice thermal conductivity. In the end, a high device zT of similar to 0.64 at 600 K with a calculated conversion efficiency similar to 8% is realized in the grain size-optimized Te0.94Se0.04As0.02 alloys, about 60% and 45% increments over that of the initial Te0.98As0.02 sample, respectively. The peak zT is maintained at similar to 1.0 at 600 K. The strategy used here should be instructive for optimizing the TE properties of other materials with remarkable grain boundary scattering.