Impact of A-site cation substitution on the properties of pinel AY₂O₄ (A = Cd, Zn): A first-principles investigation

This study presents a comprehensive first-principles investigation of the structural, electronic, magnetic, elastic, thermodynamic, and optical properties of spinel-type compounds CdY₂O₄ and ZnY₂O₄ using density functional theory (DFT) within the full-potential linearized augmented plane wave (FP-LAPW) method. Structural optimization, performed through Murnaghan equation of state fitting and internal atomic relaxation, reveals that both compounds favor a nonmagnetic normal spinel configuration as their ground state. Electronic band structure calculations using PBE-GGA and TB-mBJ functionals demonstrate that both ZnY₂O₄ and CdY₂O4 are direct band gap semiconductors, with wide band gaps ranging from 4.86 to 4.93 eV. Elastic constants confirm mechanical stability, with CdY₂O₄ exhibiting ductile behavior and ZnY₂O₄ displaying higher stiffness but slightly brittle characteristics. Thermodynamic properties, evaluated via the quasi-harmonic Debye model, indicate that both materials maintain structural integrity up to 1200 K and 20 GPa, with ZnY₂O₄ showing superior thermal stability. Optical analyses reveal strong ultraviolet absorption, high transparency in the visible range, and low reflectivity, positioning these materials as promising candidates for UV optoelectronic applications, including UV filters, transparent conductive coatings, and window layers in tandem solar cells. The results highlight that cation substitution at the A-site (Cd²⁺ versus Zn²⁺) significantly influences the mechanical, thermal, and optical properties, making CdY₂O₄ and ZnY₂O₄ attractive for next-generation photovoltaic and photonic devices.