Structural, optoelectronic and thermal response of new stable MgBe2X2 (X = As, P) Zintl phases: First-principles calculation

•Investigation of the electronic, optical and transport properties of Zintl-Phase MgBe2X2 (X = As, P) is done by first-principles calculations.•The electronic band structure and density of states (DOS) show the semiconductor nature of both compounds.•The optimized energy-volume curves, negative formation energies and phonon dispersion curves confirm the stability of the studied compounds.•A high figure of merit and stability of the Seebeck coefficient at high temperatures for both compounds with increasing power factor make them efficient compounds for thermoelectric devices. Highly-accurate computational predictions of suitable thermoelectric materials have sparked interest in discovering new Zintl phases. We report a detailed first-principles study to investigate the ground-state structural, electronic, optical and thermoelectric properties of MgBe2X2 (X = As, P) Zintl phases. Both compounds' optimized energy-volume curves, negative formation energies and phonon dispersion curves confirm their stability. A semiconductor nature is observed with bandgap values of 1.04 eV and 1.20 eV for MgBe2As2 and MgBe2P2, respectively. The optical response of the studied phases shows their potential to use in optoelectronic devices. Semi-classical Boltzmann theory is implemented through BoltzTraP code to calculate the thermal response. High Seebeck values are achieved at room temperature as well as at high temperatures. The power factor also shows an increase with the temperature increase. Furthermore, the figure of merit (ZT) shows good value of 0.74 for MgBe2As2 and 0.75 for MgBe2P2. A good optical and thermoelectric response of the studied phases opens the opportunity to use them in optoelectronic and thermoelectric applications.