First‐Principles Prediction of Enhanced Thermoelectric Properties of TaXY Janus Monolayers (X = S, Se; Y = O, N, P)

ABSTRACT Two‐dimensional Janus materials have attracted considerable attention owing to their intriguing structural, electronic, thermal, and optical properties. In this work, density functional theory calculations were employed to systematically investigate the stability, thermal transport, electronic, vibrational, and optical properties of TaXY monolayers (X = S, Se and Y = O, N, P). Cohesive energy calculations confirm the thermodynamic stability of all considered Janus monolayers. Mechanical stability analysis reveals that TaSO and TaSeO are mechanically unstable, while phonon dispersion calculations demonstrate that only TaXO and TaXN monolayers are dynamically stable, whereas TaXP monolayers exhibit dynamical instability. The lattice thermal conductivity of the stable TaSN and TaSeN monolayers was investigated using both the Slack model and first‐principles phonon Boltzmann transport calculations implemented in Phono3py. The calculated lattice thermal conductivities at 300 K are 9.55 W/mK for TaSN and 6.99 W/mK for TaSeN. The comparatively lower thermal conductivity of TaSeN originates from enhanced anharmonic phonon scattering, reduced phonon group velocity, and stronger acoustic–optical phonon interactions induced by the heavier Se atom. Furthermore, the thermal conductivity decreases with increasing temperature due to enhanced phonon–phonon Umklapp scattering. Electronic transport calculations reveal that TaSeN exhibits superior thermoelectric performance compared with TaSN, achieving a maximum figure of merit (ZT) of 2.35 at 700 K. Vibrational analysis indicates that the metallic TaXO monolayers suppress Raman activity, whereas the semiconducting TaXN monolayers exhibit distinct Raman‐active modes. In addition, frequency‐dependent optical properties, including dielectric function, refractive index, optical conductivity, absorption coefficient, loss function, and reflectivity, highlight the promising optoelectronic potential of these Ta‐based Janus monolayers. The present findings suggest that TaSeN is a promising candidate for thermoelectric and nanoscale thermal management applications.