Stable two-dimensional pentagonal tellurene: A high ZT thermoelectric material with a negative Poisson’s ratio

Abstract

Motivated by the recent experimental exfoliation of tellurium thin film, and the amazing physical and chemical properties of various theoretically tellurene allotropes, we design a novel and stable pentagonal structure of tellurene (SP-type Te), and make a detailed comparison with other possible Te allotropes, related to their mechanical, electronic and thermoelectric properties. SP-type Te shows the higher expandability than other Te allotropes, due to its lower layer modulus and Young’s modulus. More interestingly its Poisson’s ratio along x (y) direction is unusually negative (~ −0.01) which can be further decreased by applying coaxial strain. Three-layers SP-type Te can turn into a topological insulator (TI) with a nontrivial band gap ~ 0.03 eV when uniaxial compressional strain σx = −7%. Moreover the higher the number of layers in SP-type Te, the lower σx inducing its topological transition requires. At room temperature, lattice thermal conductivity kL of SP-type Te is the lowest in all Te allotropes, and meanwhile its peak ZT for n-type doping even can reach up to 2.84. Thus if SP-type Te can be synthesized in future, these extraordinary properties would promote it with great potential in designing low-dimensional mechanical, spintronic and thermoelectric devices.