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 CaIn2P2 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 (Eg) of 1.10 eV that comes from the polyanion (In2P2)−2. CaIn2P2 exhibit a mixture of flat and dispersive energy bands in the energy window from −Eg/2 to Eg/2 eV, which is a required characteristic for high electrical transport coefficients. The computed lattice thermal conductivity for CaIn2P2 is equal to 1.34 Wm−1K−1 at 900 K and 0.70 Wm−1K−1 at 1250 K. This relatively low lattice thermal conductivity of CaIn2P2 can be mainly attributed to its layered crystalline structure. The highest value of the figure of merit of CaIn2P2, viz. ZT = 0.73 (0.71), is obtained for an optimal electron (hole) concentration of 6.0×1019cm−3 (1.5×1019cm−3) at 900 K.