First principle examination of two dimensional rare-earth metal germanide halides Y2GeX2 (X = Cl, Br, I) for thermoelectric applications

Abstract

In the present work electronic, structural and thermoelectric properties of newly designed layered rare-earth metal germanide halides such as Y2GeX2 (X = Cl, Br, I) are investigated. These materials are indirect band gap semiconductors with narrow band gap 0.30 eV for Y2GeCl2,0.36 eV for Y2 GeBr2, and 0.41 eV for Y2GeI2 respectively. First principles method along with Boltzmann transport equations (BTE) is utilized together to analyse the thermoelectric properties. These materials are dynamically and mechanically stable. Thermoelectric coefficients such as electrical conductivity, seebeck coefficient and thermal conductivity are computed and put together to ultimately get the Figure of merit (ZT). Y2GeI2 has highest figure of merit (ZT) of 0.42 with Seebeck coefficient 532.12 VK−1, electrical conductivity 8.6 ×105Sm−1 and has lowest lattice thermal conductivity value of 5.55 Wm−1K−1 among three materials, which is necessary to achieve high figure of merit. The computed value of Figure of merit 0.07, 0.22 and 0.42 for Y2GeCl2, Y2GeBr2 and Y2GeI2 accordingly, shows that these materials can be considered as good candidates for energy harvesting in thermoelectric applications.