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 (E_g) 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 $-E_g/2$ to $E_g/2$ eV, which is a required characteristic for high electrical transport coefficients. The computed lattice thermal conductivity for CaIn₂P₂ is equal to $1.34\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ at 900 K and $0.70\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ 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 $6.0\times {10}^{19}\mathrm{c}{\mathrm{m}}^{-3}$ ($1.5\times {10}^{19}\mathrm{c}{\mathrm{m}}^{-3}$) at 900 K.

KEYWORDS:

• Layered Zintl phase
• first-principles calculations
• band structure
• effective mass
• transport coefficients

Acknowledgement

This work was funded by the Algerian General Directorate of Scientific Research and Technological Development (DGRSDT)/MESRS.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Algerian General Directorate of Scientific Research and Technological Development.