Transport properties of mixed CuAl(S1−xSex)2 as promising thermoelectric crystalline materials

The semi-classical Boltzmann theory as implemented in the BoltzTraP code is used to study the influence of substituting S by Se in the mixed CuAl(S1−xSex)2 crystalline materials on the transport properties. The carrier concentration (n), electrical conductivity (σ/τ), Seebeck coefficient (S), electronic thermal conductivity (κe/τ), the electronic power factor (S2σ/τ), and the figure of merit (ZT) as a function of temperature at certain value of chemical potential are calculated. The carrier concentration, electrical conductivity, electronic thermal conductivity and the electronic power factor increase exponentially with increasing temperature. CuAl(S0.75Se0.25)2 exhibits the highest n, σ/τ, κe/τ and S2σ/τ among these compounds along the whole temperature scale. We should emphasize that S is positive for all compounds which represents p-type concentration. At room temperature CuAl(S0.25Se0.75)2 and CuAl(S0.5Se0.5)2 exhibit ZT very close to unity, which implies that these materials could be good candidates for thermoelectric applications. The state-of-the-art full potential linear augmented plane wave (FPLAPW) method is used to calculate the electronic band structure, density of states and energy gaps for CuAl(S1−xSex)2. The electron effective mass ratio (me⁎/me) and effective mass of the heavy holes (mhh⁎/me) and light holes (mlh⁎/me) around Γ point, the center of the BZ, for CuAlS2 and CuAlSe2 are calculated.