Physical properties of fluorine based perovskites for vacuum-ultraviolet-transparent lens materials

Density functional theory (DFT) is used to study the bonding nature as well as the structural, electronic, and optical properties of the SrLiF3, SrNaF3, SrKF3 and SrRbF3 fluoroperovskite compounds. The findings are based on the total energy calculations where the Khon Sham (KS) equation is solved by means of an ab-initio full-potential linearized augmented plane wave (FP-LAPW) method. The structural properties including the lattice constant (a(o)), ground state energy (E), bulk modulus (B), and their pressure derivative (B ') are evaluated using the Local Density Approximation (LDA) and the Generalized Gradient Approximation (GGA) exchange correlation potential. Furthermore, to avoid the underestimation of the band profile by other DFT schemes we highlight the GGA plus Trans-Blaha modified Becke-Johnson (TB-mBJ) potential in lieu of attaining opto-electronic trends close to the expected experimental findings. Detailed analysis of the band dispersion curves is done with five different exchange and correlation schemes at the (Gamma-Gamma), (R-R), (M-M) and (X-X) symmetry points. A predominant characteristic associated with cation replacement shows that Li by Na, Na by K, and K by Rb significantly reduce the direct bandgap in these compounds. This crucial variation is responsible for working in different UV regions of the spectrum. The calculations of the band structure show that these compounds have a wide and direct energy bandgap at (Gamma-Gamma). The total and partial density of state curves are used to define the contributions of the different bands. In addition to this, contour plots of the electron density verify that the ionic behavior increases as we go from SrLiF3 to SrRbF3 while the brittleness, which dominates in them, decreases from SrLiF3 to SrRbF3. To verify the opto-electronic behavior bandgap dependent optical parameters, such as the complex dielectric function epsilon(omega), optical conductivity sigma(omega), energy loss function L(omega), and effective number of electrons n(eff), the sum rules are analyzed. All the calculated results are in favorable agreement with the previous theoretical and existing experimental data. Furthermore, the opto-electronic properties from the (TB-mBJ) potential are reported, which reveals that the fluorine based strontium series of perovskites are wide and direct band gap ionic insulators. The comprehensive present methodology represents an effective and influential tool for calculating the whole set of opto-electronic parameters, which can provide support for the understanding of various physical phenomena and empower device engineers for implementing these materials in UV based devices. (C) 2017 The Physical Society of the Republic of China (Taiwan). Published by Elsevier B.V. All rights reserved.