First-principles prediction of enhanced thermoelectric properties of double transition metal MXenes: Ti3−xMoxC2T2;

Employing first-principles electronic structure calculations, we investigate the stability, electronic, and magnetic properties of ordered double transition metal-based two-dimensional maxene (MXene) compounds, ${\mathrm{Ti}}_{3\ensuremath{-}x}{\mathrm{Mo}}_{x}{\mathrm{C}}_{2}\phantom{\rule{0.28em}{0ex}}(x=0.5,1,1.5,2,2.5)$. Both unpassivated and compounds passivated with -OH, -O, or -F are considered. Based on this investigation, three narrow gap semiconducting compounds are identified, namely, ${\mathrm{Ti}}_{2}{\mathrm{MoC}}_{2}{\mathrm{F}}_{2},\phantom{\rule{0.28em}{0ex}}{\mathrm{TiMo}}_{2}{\mathrm{C}}_{2}{\mathrm{F}}_{2}$, and ${\mathrm{TiMo}}_{2}{\mathrm{C}}_{2}{(\mathrm{OH})}_{2}$ for subsequent study of thermoelectric properties within the formalism of Boltzmann transport. Our paper highlights the potential of ${\mathrm{Ti}}_{2}{\mathrm{MoC}}_{2}{\mathrm{F}}_{2}$ as a thermoelectric material with a ZT value higher than 1 within a large temperature range of 300--800 K upon $p$-type carrier doping. The ZT value of $p$-type ${\mathrm{Ti}}_{2}{\mathrm{MoC}}_{2}{\mathrm{F}}_{2}$ is found to reach a high value of 3.1 and an efficiency of $\ensuremath{\sim}27%$ at 800 K. Our exercise should motivate experimental study of yet-to-be synthesized double transition metal MXene compound, ${\mathrm{Ti}}_{2}{\mathrm{MoC}}_{2}$.