Origin of the optical anisotropy and the electronic structure of Ru-based double perovskite oxides: DFT and XPS studies

Abstract

Experimental and theoretical studies of the electronic structure of Pr₂LiRuO₆ (PLR), Nd₂LiRuO₆ (NLR) and Sm₂LiRuO₆ (SLR) crystals are reported. The linear optical properties of these compounds have been investigated using density functional theory calculations. The optical anisotropy in these compounds is revealed from their computed optical properties, such as their complex dielectric functions and refractive indices. The calculations show that SLR has a relatively large birefringence (Δn = 0.06) compared to NLR and PLR, which is important for mid-infrared nonlinear optical applications. We propose that the O 2p to Ru 4d transition is primarily responsible for the origin of optical activity in these materials while the origin of the optical anisotropy in these materials results from the asymmetrically oriented Ru–O bonds in the RuO₆ octahedra of the unit cell. The evolution of the Ru 3d core-level signals as obtained from the X-ray photoemission spectroscopy measurements provide confirmation of a dynamic increment in the electron correlations as we move from PLR and NLR to SLR.