Topological properties of a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si63.svg" display="inline" id="d1e1380"> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">BiSbSe</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>3</mml:

Motivated by the recent synthesis of a BiSbSe 2 . 5 Te 0 . 5 alloy and its intriguing properties (Goncalves et al., 2019), we employ ab-initio calculations to study the structural, electronic and topological properties of a BiSbSe 3 − x Te x alloy as a function of the Te content x . We employ two complementary approaches: the virtual crystal approximation (VCA), which captures the average effects of the Se/Te substitution, and the supercell approximation, which gives specific details about different alloy concentrations. We find that all structures are strong topological insulators, exhibiting the characteristic band inversion in the bulk band structure and surface states with linear dispersion inside the band gap. The properties of these states, such as the band gap, the Fermi velocities and the relative position of the Dirac cones, are found to be very tunable with x , as a result of an interesting interplay between the effects of spin–orbit interaction and an intrinsic electric polarization, which is induced by symmetry breaking due to the presence of non-equivalent Bi and Sb atomic planes. We also find that states at the top and bottom surfaces of a slab are different due to the proximity of each surface to a Bi or Sb plane and to different distributions of Se and Te atoms over the structure. These results reveal the great versatility of these alloys and show great promise for applications in future nanoelectronic and spintronic devices. • New topological insulators can be made by constructing BiSbSe 3 − x Te x • Topological properties can be tailored by Se/Te concentration • Spin–orbit coupling (SOC) is increased by Te content • BiSbSe/Te alloys have an intrinsic polarization • Interplay of SOC and polarization results in a modulation of topological properties.