Fracture structure and thermoelectric enhancement of Cu2Se with substitution of nanostructured Ag2Se

Abstract

Recently, copper chalcogenides have attracted great attention due to their potential application for mid- to high-temperature thermoelectric power generation. In this work, we report the thermoelectric properties of Cu₂Se compounds with different sample preparation processes and the inclusion of a nanoscale Ag₂Se powder synthesized with a unique wet chemistry procedure. The Cu₂Se compounds were prepared by solid state reaction (SSR), fast quenching (FQ) and mechanically alloyed with nanostructured Ag₂Se (NM) followed by hot pressing. High temperature transport properties were assessed by the Seebeck coefficient, electrical conductivity and thermal conductivity measurements. Structural characterization demonstrates that the nano-Ag₂Se included sample is multi-phase with several nanoscale features not seen in the Cu₂Se samples prepared in the standard method. As a result, the Cu₂Se-NM sample possesses a miniscule thermal conductivity, with values as low as 0.5 W m⁻¹ K⁻¹. Fortunately, the nano-inclusions present in the Cu₂Se-NM sample do not significantly disrupt electronic transport, preserving the power factor at a consistently high value over a broad range of temperatures. Consequently, the nano-Ag₂Se included sample exhibits large average ZT values and a maximum of 1.85 at 800 K that rivals some of the best thermoelectrics currently available. Here, we present microstructural and transport evidence that the wet chemistry technique implemented in our study enables the optimization of thermoelectric performance in superionic conductor Cu₂Se.