Unraveling the relationship between bulk structure and exposed surfaces and its effect on the electronic structure and photoluminescent properties of Ba0.5Sr0.5TiO3: A joint experimental and theoretical approach

In this paper, we conducted a combined experimental and theoretical investigation of bulk and (001) surface properties of a Ba_0.5Sr_0.5TiO₃ (BST) material synthesized by the polymeric precursor method. Characterization techniques, such as X-ray diffraction (XRD), Raman spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, field-emission scanning electron microscopy (FE-SEM) and photoluminescence (PL), were employed to disclose the structural, electronic, and optical properties of BST. Structural analysis confirmed the BST tetragonal symmetry, showing the relevant fingerprints of structural distortions, while the crystallographic morphologies were observed in the FE-SEM images. The theoretical results evidenced the structural disorder along the tetragonal BST phase, corroborating the central role of the bonding environment in the electronic and PL properties of the material. Moreover, the (001) surface results indicated that E_surf values depend on the chemical environment of exposed surfaces following the bonding character along with A-O and Ti-O paths, which also affects the electronic structure of surface-oriented BST.