Computational investigation of the phase stability, electronic, optical, phonon spectrum, and elastic behavior of layered perovskites Ca2XO4 (X = Zr, Hf) for optoelectronic applications

Abstract

Context: A significant class of solid-state materials, Ruddlesden-Popper (RP) perovskites are well-known for their rich chemical compositions that make them excellent electrocatalysts. Therefore, in this work, we conduct thorough analysis of RP perovskites, specifically Ca₂XO₄ (X = Zr, Hf). We delve into the structural, electronic, optical, and mechanical properties presenting their insights for the first time. Our investigations reveal that Ca₂XO₄ (X = Zr, Hf) exhibits stable tetragonal phase structures, with energies (E₀) of - 10,522.93 eV and - 33,520.14 eV, respectively. The calculated $E_{\mathrm{cohsive}}/\mathrm{atom}$ in terms of the ground state determines to possess distinct values such as - 4.79 eV/atom for LiScTe₂ and - 3.95 eV/atom for Ca₂ZrO₄ and Ca₂HfO₄. Notably, the semiconductor characteristics of Ca₂ZrO₄ and Ca₂HfO₄ are underscored by their respective wide direct band gap of 5.02 eV and 5.30 eV. Then, we discuss the optical parameters encompassing the dielectric function, absorption coefficient, optical conductivity, refractive index, and energy loss function. ${\mathrm{Ca}}_2{\mathrm{ZrO}}_4$ is described as ductile, whereas ${\mathrm{Ca}}_2{\mathrm{HfO}}_4$ is defined as brittle. Our outcomes underscore remarkable ability of these materials to absorb ultraviolet radiation from the electromagnetic spectrum, positioning them as promising candidates for optoelectronic applications.

Methods: We made these calculations by employing first-principles approach rooted in density functional theory (DFT) and utilizing the Perdew-Burke-Ernzerhof-Generalized Gradient Approximation (PBE-GGA) and Tran and Blaha-modified Becke-Johnson (TB-mBJ) functional within the WEIN2K framework. In this framework, Kramers-Kronig relations are used to obtain crucial optical parameters. Mechanical behavior is assessed by employing Voigt-Reuss-Hill approximation (VRH) fulfilling the Born's criteria which emphasizes that these materials are equally appropriate for a broad range of mechanical applications.

Keywords: Absorption; Electronic; Optical; Semiconductor; Ultraviolet.