GeAs: Highly Anisotropic van der Waals Thermoelectric Material

GeAs
and Sn-doped GeAs were synthesized from elements. Both crystallize
in a layered crystal structure in the C2/m space group (No. 12) in the GaTe structure type. The crystal
structure consists of As-terminated layers separated by van der Waals
gaps. 119Sn Mössbauer spectroscopy reveals that
in the doped compound, Sn atoms are situated in a symmetric and homogeneous
environment, most probably in the form of Sn2 dumbbells.
The anisotropic crystal structure of GeAs leads to highly anisotropic
transport properties. High electrical and thermal conductivities were
determined along the crystallographic layers. For the perpendicular
direction across the layers, a sharp drop of more than an order of
magnitude was observed for the transport properties of the GeAs single
crystal. As a result, an order of magnitude difference in the figure
of merit, ZT, was achieved. High-temperature thermoelectric
characterization of the Sn-doped compound reveals a remarkable ZT with a maximum of 0.35 at 660 K.