Electronic and thermoelectric properties of the layered Zintl phase CaIn2P2: first-principles calculations

Abstract

We have studied the doping concentration dependence of the thermoelectric (TE) properties for the n- and p-doped CaIn<inf>2</inf>P<inf>2</inf> layered Zintl phase at two fixed temperatures: T = 600 and 900 K through first-principles electronic band structure calculations combined with Boltzmann's transport theory within charge-carrier relaxation time and rigid band approximations. The band structure calculated using the Tran-Blaha modified Becke–Johnson potential shows a fundamental indirect energy band gap (E <inf>g</inf>) of 1.10 eV that comes from the polyanion (In<inf>2</inf>P<inf>2</inf>)−2. CaIn<inf>2</inf>P<inf>2</inf> exhibit a mixture of flat and dispersive energy bands in the energy window from (Formula presented.) to (Formula presented.) eV, which is a required characteristic for high electrical transport coefficients. The computed lattice thermal conductivity for CaIn<inf>2</inf>P<inf>2</inf> is equal to (Formula presented.) at 900 K and (Formula presented.) at 1250 K. This relatively low lattice thermal conductivity of CaIn<inf>2</inf>P<inf>2</inf> can be mainly attributed to its layered crystalline structure. The highest value of the figure of merit of CaIn<inf>2</inf>P<inf>2</inf>, viz. ZT = 0.73 (0.71), is obtained for an optimal electron (hole) concentration of (Formula presented.) ((Formula presented.)) at 900 K. © 2020 Elsevier B.V., All rights reserved.