Strain engineering and thermoelectric performance of Janus monolayers of titanium dichalcogenides: A DFT study

Abstract

By employing state-of-the-art density functional theory calculations, we have investigated the effect of compressive and tensile strain on the electronic and transport properties of recently invented Janus monolayers of 1 T TiXY (X, Y = S, Se, Te). The lattice dynamics studies reveal that the monolayers of TiSSe are stable up to a tensile strain of 4 %, whereas TiSTe and TiSeTe monolayers are stable up to 10 % tensile strain. The compressive strain leads to appearance of imaginary phonon frequencies indicating the instability of these monolayers against compressive strain. Our results predict that the strain engineering has a favorable impact on the electronic band structure. According to our findings, with increase in biaxial tensile strain on all the studied monolayers the Seebeck coefficient increases and the electronic thermal conductivity reduces which results in improved ZT. The obtained ZT values at highest tolerable tensile strains for these monolayers are found to be 1.04, of 0.95 and 0.88 for TiSSe, TiSTe and TiSeTe respectively. Further, the spin orbit coupling does not have any significant effect on electronic properties. Thus, our study predicts that biaxial strain can drastically enhance thermoelectric performance of the studied Janus monolayers. Hence, these materials have the potential to find use in nanoscale optoelectronic and thermoelectric devices.