GeAs: Highly Anisotropic van der Waals Thermoelectric Material

Abstract

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. 119 Sn Mossbauer spectroscopy reveals that in the doped compound, Sn atoms are situated in a symmetric and homogeneous environment, most probably in the form of Sn 2 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 Sndoped compound reveals a remarkable ZT with a maximum of 0.35 at 660 K.

Chemical and Electrochemical Lithiation of van der Waals Tetrel‐Arsenides

“…Binary GeAs and SiAs compounds, which have been known for decades, have mostly been overlooked in terms of properties until recently . These isostructural compounds are built of covalently bonded Si‐As or Ge‐As layers held together by weak van der Waals interactions.…”

“…These isostructural compounds are built of covalently bonded Si‐As or Ge‐As layers held together by weak van der Waals interactions. Resistivity and thermal conductivity property measurements on oriented single crystals reveal that the transport properties are anisotropic, reflecting the anisotropic nature of the structures . The layered covalent structure may be a suitable host system for possible insertion of small cations in analogy to Li intercalation in graphite.…”

“…Layered tin phosphide, Sn 4 P 3 , has been studied for lithium‐ion and sodium‐ion battery applications and has been proven to be a promising material . Pnictides of lighter tetrels such as GeAs, SiAs, GeP, SiP, GeAs 2 , and SiAs 2 have been gaining interest in the field of thermoelectrics, photovoltaics, water splitting, and optics owing to their anisotropic nature, weak interlayer interactions, relatively small band gaps (<2 eV), and potential for tuning of properties through doping and strain …”

Emerging nanostructured electrode materials for water electrolysis and rechargeable beyond Li-ion batteries

“…SiP, SiAs, GeP, and GeAs are isostructural and crystallize in the GaTe structure type [183][184][185][186]. Within each layer, Si-Si (Ge-Ge) pairs are surrounded by six P atoms forming a distorted trigonal antiprism.…”

“…Si and Ge pnictides exhibit properties typical for the van der Waals solids, such as strong anisotropy of the thermal and electrical transport properties and exfoliation upon applying mechanical or chemical forces [185,186]. They were proposed as promising anodes for Li intercalation electrodes [190].…”