Antimony arsenide: Chemical ordering in the compound SbAs

TL;DR

This study reveals that the semimetallic compound SbAs exhibits chemical ordering of Sb and As within its rhombohedral A7 structure, affecting its electronic properties and phase transition behavior.

Contribution

It demonstrates the presence of chemical ordering in SbAs, previously thought to be randomly mixed, using advanced diffraction and analysis techniques.

Findings

Sb and As are ordered in the A7 structure of SbAs.

An ordering transition occurs around 550 K.

SbAs remains a semimetal with a larger direct band separation.

Abstract

The semimetallic Group V elements display a wealth of correlated electron phenomena due to a small indirect band overlap that leads to relatively small, but equal, numbers of holes and electrons at the Fermi energy with high mobility. Their electronic bonding characteristics produce a unique crystal structure, the rhombohedral A7 structure, which accommodates lone pairs on each site. Here we show that the A7 structure can display chemical ordering of Sb and As, which were previously thought to mix randomly. Our structural characterization of the compound SbAs is performed by single-crystal and high-resolution synchrotron x-ray diffraction, and neutron and x-ray pair distribution function analysis. All least-squares refinements indicate ordering of Sb and As, resulting in a GeTe-type structure without inversion symmetry. High-temperature diffraction studies reveal an ordering transition around 550 K. Transport and infrared reflectivity measurements, along with first-principles calculations, confirm that SbAs is a semimetal, albeit with a direct band separation larger than that of Sb or As. Because even subtle substitutions in the semimetals, notably Bi_{1-x}Sb_x, can open semiconducting energy gaps, a further investigation of the interplay between chemical ordering and electronic structure on the A7 lattice is warranted.