Investigation of electronic, mechanical, dynamic and optical properties of LnScO3(Ln = Eu, La, Nd, Sm, Pr, Tb) compounds : AB initio calculation

In this thesis, the structural, electronic, mechanical, vibrational, thermodynamic and optical properties for rare-earth scandate LnScO3 (Ln= Eu, La, Nd, Pr, Sm, Tb) compoundsin orthorhombic structure were investigated using ab inito method within GGA and GGA+U approaches. The dependence of the physical quantities of LnScO3 compounds on the Hubbard-U correction parameter value (0 < U ≤ 10 eV) was examined in detail. The density of state and electronic band structure calculations showed that LnScO3 compounds are an insulating material and have a direct electronic band gap at the Γ-Γ point. The GGA (+U) calculations show that there is strong hybridization between the Sc-3d and O-2p states. Rare-earth (Ln)-5d states contribute somewhat to this hybridization. The electronic charge distribution, (P)DOS and BEC calculation results show that the binding behavior of LnScO3 compounds is a combination of covalent and ionic nature. The calculated elastic constants show that these compounds have mechanical stability. Bulk, shear and Young's modulus, Poisson's ratio, anisotropy factor, sound velocity and Debye temperature were calculated for both GGA and GGA+U using elastic constants. The phonon dispersion curves and phonon state densities of the compounds were calculated and since all phonon vibrational modes of the compounds are positive in the Brillouin region, these compounds are dynamically stable. Thermodynamic properties of compounds such as entropy, heat capacity, internal energy and free energy were investigated. Our results show that the structural and electronic properties are affected by the application of the Hubbard-U term in GGA calculations and the calculated lattice constants, bond length and bond angles deviate more from the experimental values, while the electronic band gap approaches the experimental values.