Crystal structure, stability, and transport properties of Li₂BeAl and Li₂BeGa Heusler alloys: a DFT study

In this study, the structural, elastic, electronic, and thermoelectric properties of full Li₂BeAl and Li₂BeGa Heusler alloys were explored using density functional and the Boltzmann transport theories. The GGA and HSE approximations have been used for the exchange-correlation potential. Results indicated that these two compounds are more energetically stable in the inverse Heusler structure. Additionally, both Li₂BeAl and Li₂BeGa Heusler alloys were found to be mechanically stable due to the positive values of the elastic constants. Also, the high values of the Young's modulus indicate that these compounds are stiff and exhibit a semi-metallic nature. The band gaps were determined to be 0.13 eV and - 0.22 eV for Li₂BeAl and Li₂BeGa alloys, respectively, using the GGA approximation. By employing the HSE hybrid functional, however, the band gap for Li₂BeAl increased to 0.26 eV, and for Li₂BeGa, it decreased to - 0.16 eV. Regarding thermoelectric properties, Seebeck coefficient, electrical conductivity, electronic and lattice thermal conductivities, power factor, and the figure of merit have been calculated for both Li₂BeAl and Li₂BeGa Heusler alloys at different temperatures. Seebeck coefficient in both alloys decreases with increasing the temperature and has the highest value at 300 K. Thermal conductivity and electrical conductivity increase with increasing the temperature, which confirms the intermetallic behavior of the Heusler alloys. The results obtained for both alloys show that n-type doping has better thermoelectric properties than p-type doping. The maximum value of the figure of merit (ZT) was obtained for n-type doping, which was 1.43 at 660 K for Li₂BeAl and 0.39 at 1000 K for Li₂BeGa alloy. The high values of ZT especially for electron-dopped Li2BeAl suggest the great potential of this material for use in thermoelectric devices. This study suggests that the proposed materials have potential applications in spintronic devices and thermoelectric materials due to their intermetallic character and effective thermoelectric coefficients.