Strain engineered thermodynamic stability, electronic and thermoelectric characteristics of TiB₂ and ZrB₂ monolayers

The thermodynamic stability, electronic, and thermoelectric properties of TiB₂ and ZrB₂ are computed using density functional and Boltzmann transport theory. The phonon band dispersion of ZrB₂ monolayer exhibits dynamic instability with the presence of imaginary frequency. The small direct bandgap is noticed for these monolayers. More interestingly, the biaxial strain improves the dynamic stability of ZrB₂ monolayer. In addition, the electronic properties are not changing significantly for the considered monolayers. The strain modulated Seebeck coefficient, electrical conductivity, and electronic thermal conductivity are investigated to understand the thermoelectric properties. The Seebeck coefficient is reducing while electrical conductivity and electronic thermal conductivity are improving with increasing temperature. The Seebeck coefficient is decreasing with increasing the biaxial tensile strain. Moreover, the electrical conductivity and electronic thermal conductivity values are increasing with the increasing strain. Further, a very large lattice thermal conductivity is observed for TiB₂ monolayer as compared to ZrB₂ monolayer. Thus, strain can be used to enhance the dynamic stability and modulate the thermoelectric properties of such systems and TiB₂ monolayer may be a potential low temperature efficient thermoelectric material because of its small bandgap and high thermal conductivity at low temperatures.