Investigation of Physical Properties of NaBaX3 (X = Cl, Br, and I) Cubic Perovskites Using First-Principles Density-Functional Theory

The study investigates the physical properties of cubic perovskites NaBaX₃ (X = Cl, Br, and I) through first-principles calculations to observe the potential for optoelectronic applications. Each of the compounds NaBaX₃ (X = Cl, Br, and I) shows an indirect semiconducting band gap of 3.88 eV, 2.85 eV, and 2.80 eV, respectively, considering they are held together by ionic and covalent bonds. The negative formation enthalpy, positive pressures, and Born stability confirm that the structure remains stable for each compound. They also prove to be both ductile and anisotropic, with NaBaI₃ being more machinable and NaBaCl₃ having a higher melting point as well as higher predicted electrical conductivity from Debye temperature analysis. Strong absorption of ultraviolet (UV) light and a drop in reflectivity are noticed in the areas where the energy loss peaks, making such materials potential UV detectors, scintillators, and protective UV coatings. When viewing phonon dispersion plots, it is evident that the phases may transform because of negative phonon frequencies and tolerance factor differences. Tests report weak thermal conductivity with 0.0159 W/mK, 0.0114 W/mK, and 0.0081 W/mK for the compounds NaBaCl₃, NaBaBr₃, and NaBaI₃, respectively, which makes their use as insulators in optoelectronics very suitable. The fact that entropy–energy relationships and heat capacity values are close to the Dulong–Petit limit with values of 17–18 J/mol·K indicates these materials will perform consistently in thermal conditions. Summarizing everything, NaBaX₃ (X = Cl, Br, and I) perovskites have a stable structure, absorb UV light, and their properties can be changed mechanically and thermally, which is ideal for future photovoltaic and optoelectronic devices.