To study the structural, electronic, and optical properties of lead-free Barium titanate BaTiO₃ (BT) ferroelectric material in its tetragonal structure, a combination of experimental and theoretical studies has been used and the obtained results were discussed. The studied BT compound was prepared via the sol–gel technique. The calculated bandgap energy (E_g) and structural parameters of BT are determined using four types of exchange–correlation functionals (PBE, PBEsol, LDA, and PW91) in the perspective of the density functional theory (DFT). XRD and Raman analysis have shown that BT ceramic exhibits a tetragonal phase structure without any trace of impurity phases. The UV–vis investigation showed that BT has a bandgap energy of 3.19 eV, which is larger than the theoretically calculated values. The computed lattice parameter c is overestimated (as large as ~1% deviation) when using the LDA approximation. In contrast, PBEsol proved that those lattice constants were close to the experimental values (a deviation of less than 1%).

In this research, ceramic bricks were produced based on natural zeolite from Tokaj (Hungary) using the dry pressing technique. The microstructure, morphology and properties of the produced samples were examined via scanning electron microscopy, X-ray diffraction and X-ray fluorescence. The X-ray investigation revealed various minerals in the natural zeolite; moreover, the samples’ physical and thermal properties were also investigated. The sintering temperature and composition play a major role in the microstructure and the properties of the prepared ceramic samples. The produced ceramics bricks have excellent thermal insulation and good mechanical strength. The results of this research work confirm the potential use of natural zeolite from Tokaj as an eco-friendly building material.