Structural, elastic, electronic and optical properties of some Ruddlesden–Popper compounds

The structural, elastic, electronic and optical properties of Ruddlesden–Popper-layered (Sr,Ca)₃Ti₂O₇ compounds in the paraelectric phase have been studied in detail using a first-principles method based on density functional theory. The results obtained from structural optimization demonstrate that they are consistent with existing experimental and theoretical results in the literature. To investigate the mechanical properties of the Sr₃Ti₂O₇ and Ca₃Ti₂O₇ compounds, second-order elastic constants were calculated. The obtained results confirm that the Sr₃Ti₂O₇ and Ca₃Ti₂O₇ compounds are mechanically stable. The polycrystalline elastic modulus, including bulk modulus (B), shear modulus (G), Young’s modulus (E) and Poisson’s ratio (ν), for both compounds was calculated using the obtained elastic constants. It was estimated from the calculated \({H}_{\text{macro}}\) and \({H}_{\text{micro}}\) hardness values that these compounds are medium-hard materials. Furthermore, both compounds were found to be elastically anisotropic and brittle materials. The electronic structure analysis indicates that the Sr₃Ti₂O₇ and Ca₃Ti₂O₇ compounds are semiconductor materials with indirect bandgaps of 2.92 and 2.89 eV, respectively. To determine their potential application areas in optoelectronic devices, the frequency-dependent complex dielectric function of the Sr₃Ti₂O₇ and Ca₃Ti₂O₇ compounds was calculated.