High thermopower and potential thermoelectric properties of crystalline LiH and NaH

We use first-principles calculations combinedwith the Boltzmann transport equation and semiclassical analysis to investigate the thermal conductivity., electrical conductivity sigma, and thermopower S of crystalline LiH and NaH. Remarkably, the calculated S is extraordinarily high while the lattice thermal conductivity kappa(L) is fairly low, which, as a result, leads to a much high thermoelectric power factor sigma S-2 and good thermoelectric properties, with the figure of merit zT even larger than 1.5 in the p-type doped NaH. Further analyses reveal that (i) the large band gap and the flat band around the Fermi level cause the high S and (ii) strong anharmonic phonon scatterings and relevant phonon group velocities result in the low.L in these light materials. Our results support that crystalline LiH and NaH may be potential materials for thermoelectric applications.