The Surface Effect on the Thermoelectric Property of the [001] and [111] NaMgP Films: A DFT Study

Abstract

Based on the density functional theory framework and full potential augmented plane waves plus local orbitals (FP-LAPW\u2009+\u2009lo) method with GGA-mBJ approximation, the electronic and thermoelectric (TE) properties of the NaMgP bulk and its films along the [001] and [111] directions have been calculated. The mechanical calculations including the energy–volume (E–V) diagram, elastic constants and phonon dispersion have been indicated the good stability of the NaMgP bulk in the static and dynamic view. The p-type semiconductor nature of this compound by 2.73\xa0eV direct gap has been shown the suitable merit (ZT) parameter for TE applications of 50\xa0K to 800\xa0K temperature range. Based on the surface effect in the [001] and [111] films, the NaMg termination film of [001] film, MgP and NaP terminations of the [111] have the magnetic behavior with half-metallic and magnetic semiconductors, so, their TE behaviors were sensitive to the external magnetic field. The NaMg and MgP terminations have the high amount of the ZT at the 50\xa0K and even that the room temperature for up-spin, which are suitable for power generators at higher temperatures. Also, the NaP termination has the big ZT at 50\xa0K of the up-spin that is suitable for cooling technology.