Type controlled thermoelectric properties in tin selenide fabricated using room-temperature synthesis and hot pressing

We successfully synthesized two series of single-phase nanosized SnSe at room temperature with various pH values. The resulting powders were consolidated by hot pressing at 500 degrees C under an applied pressure of 80 MPa for 1 h. The conditions of washing and preparing with different pH values significant effect the thermoelectric properties and chemical compositions. Energy dispersive x-ray spectroscopy analyses indicate that chlorine persistently exists for samples via simple washing while no chlorine is found for samples via thorough washing. Chlorine introduces electron carriers and brings about sign crossover in thermopower and negative room-temperature Hall coefficients for samples synthesized at pH = 1.4 and 6.5. Samples containing no chlorine all exhibit positive sign of thermopower throughout the investigated temperature between 300 and 800 K and positive room-temperature Hall coefficients, indicating majority carriers are holes. Among these two series of SnSe, the materials containing chlorine and no chlorine synthesized at pH = 12.3 exhibit the highest zT = 0.26 at 700 K and 0.30 at 770 K, respectively. Our approach provides an energy-saving route for fabricating SnSe with different types of majority carriers. This work may improve the applicability of SnSe-based materials in thermoelectric generators. (c) 2021 Elsevier B.V. All rights reserved.