Crystal Structure and Atomic Vacancy Optimized Thermoelectric Properties in Gadolinium Selenides

Abstract

Thermoelectric materials enable the mutual energy conversion of waste heat and electricity, critical to relieve global energy crisis. Hightemperature thermoelectric materials are special species due to their high-temperature stability and noticeable energy conversion efficiency.Here, we report a systematic investigation on high-temperature thermoelectric gadolinium selenides, cubic Gd 3-x Se 4 (x = 0.16, 0.21 and 0.25) and orthorhombic Gd 2 Se 3-y (y = 0.02, 0.06 and 0.08). High energy synchrotron x-ray diffraction and total scattering are used to investigate the crystallographic and local structures. The atomic-scale cluster of Gd vacancy in cubic Gd 2.84 Se 4 is observed by employing the reverse Monte Carlo simulation. For cubic Gd 3-x Se 4 , its carrier concentration is tuned and multiple conduction bands are incorporated by adjusting Gd vacancy. Experimentally, the gradual increase in effective masses is evidently observed in cubic Gd 3-x Se 4 , which is consistent with the density functional theory (DFT) calculation. A reasonable peak zT value of 0.27 is achieved at 850 K for Gd 2.84 Se 4 . On the other hand, adjusting Se vacancy enables the optimization of electron concentration for orthorhombic Gd 2 Se 3-y phase. Its low deformation potential (Ξ = 12eV) with single conduction band gives rise to enhanced electron mobility and higher peak zT value of 0.54 at 850 K for Gd 2 Se 2.98 . In addition, a higher zT of 1.2 at1200 K is reasonably predicted for Gd 2 Se 2.98 by using quality factor analysis. This work not just presents a systematic crystallographic investigation of gadolinium selenides, but also provides a deep insight into the charge transport and phonon scattering mechanisms. This study facilitates the exploration of more hightemperature thermoelectric materials.

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