Junaid Khan

Er-based perovskite oxides have emerged as promising multifunctional materials for photocatalytic, optoelectronic and energy-conversion applications owing to their tunable electronic and optical properties. In this work, first-principles Density Functional Theory (DFT) calculations were performed to systematically investigate the structural, electronic, elastic, thermodynamic and optical properties of cubic ErXO ₃ ([Formula: see text], Fe, Ru) perovskite oxides. Structural optimization and negative formation energies ([Formula: see text]2078.12, [Formula: see text]3496.39 and [Formula: see text]4250.99 eV for ErFeO ₃ , ErRuO ₃ and ErOsO ₃ , respectively) confirm the thermodynamic stability of all compounds. Electronic band structure calculations reveal semiconducting behavior with band gaps of 1.99 eV (ErOsO ₃ ), 2.89 eV (ErFeO ₃ ) and 3.51 eV (ErRuO ₃ ), corresponding to visible, near-ultraviolet and ultraviolet spectral regions, respectively. The calculated absorption edges at 623, 429 and 353 nm demonstrate broad spectral coverage, with ErOsO ₃ exhibiting superior visible-light absorption, making it a promising candidate for visible-light-driven photocatalytic water splitting and pollutant degradation. In contrast, ErFeO ₃ and ErRuO ₃ are more suitable for ultraviolet-assisted photocatalytic processes. Mechanical analysis confirms that all compounds satisfy the stability criteria and exhibit ductile behavior with elastic anisotropy factors of 0.79 (ErOsO ₃ ), 0.31 (ErFeO ₃ ) and 0.539 (ErRuO ₃ ), indicating favorable mechanical robustness. The enhanced optical response, together with their stable crystal structure and tunable electronic properties, highlights the potential of ErXO3 perovskite oxides as multifunctional materials for next-generation photocatalytic, optoelectronic, photovoltaic and sustainable energy-conversion technologies.

Comparative models were developed for pristine, Ni-doped, Ta-doped and Ni–Ta co-doped systems. Pristine anatase TiO ₂ exhibits a band gap of 2.12[ ]eV, Ni doping reduces the band gap dramatically to 1.02[ ]eV by introducing two isolated Ni 3d impurity states above the valence band, narrowing the band gap and extending absorption into the visible region; however, these unoccupied states act as recombination centers that limit photocatalytic efficiency. In contrast, Ta doping introduces 5d states just below the conduction band, shifts the Fermi level upward and reduces the band gap to [ ]1.80[ ]eV, indicating n-type conductivity. Notably, co-doping with Ni and Ta further reduces the band gap to [ ]1.24[ ]eV relative to Pure Tio ₂ , while simultaneously transforming the Ni 3d states into occupied ones. This suppresses recombination and improves charge carrier separation, enhancing visible-light photocatalytic activity. Optical analyses reveal that Ni doping produces the strongest visible-light absorption intensity, whereas Ni–Ta co-doping broadens the absorption range and enhances overall optical utilization. The negative formation energies obtained for all doped configurations confirm that Ni-, Ta- and Ni–Ta-doped TiO ₂ systems are thermodynamically stable under oxygen-rich conditions. Charge density and electrostatic potential analyses further reveal localized charge redistribution and internal field gradients, which promote efficient charge separation. These results suggest that Ni–Ta co-doping is a promising strategy for designing stable and highly efficient TiO ₂ -based photocatalysts for solar-driven applications.

Lithium-ion batteries (LIBs) are a promising alternative to lead–acid batteries, offering environmental benefits and cost effectiveness. Their performance depends on the development of anode materials with high theoretical capacities and rapid ion diffusion. In this study, we investigated the potential of copper silicide (Cu3Si) as an anode material for LIBs using first-principles calculations. The energy versus volume plot and phonon dispersion analysis confirm its structural stability, further supported by a negative formation energy of –1901.8[ ]eV. Electronic structure analysis revealed that Cu3Si is a semiconductor with an indirect bandgap of 1.71[ ]eV. Elastic property calculations, including the bulk modulus, Young’s modulus, shear modulus, Zener anisotropy factor, [ ] ratio and Poisson’s ratio, indicate strong mechanical stability with a soft and flexible nature compared to conventional electrode materials. Electrochemically, Cu3Si exhibits excellent cyclic and electrochemical stability, maintaining a relatively stable voltage profile with minimal polarization, good reversibility, and low overpotential. Among the calculated electrode materials, the Cu3Si composite exhibited superior cycling stability, maintaining over 70% of its initial capacity after 500 cycles. This enhanced performance is attributed to its ability to effectively buffer volumetric changes during lithiation, outperforming both silicon and commercial graphite electrodes. Similarly, voltage–capacity analysis revealed that Cu3Si offers a stable voltage profile with minimal polarization, outperforming silicon and graphite in terms of electrochemical reversibility and cycling stability. These characteristics underscore its potential as a high-performance anode material for next-generation LIBs.

Using the wien2k package in DFT, the structural, elastic, electrical, and optical characteristics of MgXCl₃ (X = Rb, Ca) were investigated. Structural analysis confirmed the stability of these compounds and revealed that they possessed a cubic structure with the space group of pm-3m 221. The electronic properties of the compounds were analyzed using band structure and density of states (DOS) calculations, revealing their semiconducting nature. To investigate the elastic properties, we examined the elastic constants, anisotropy factor, Pugh ratio, Poisson ratio, and bulk modulus. The ductility of these compounds is indicated by Pugh’s ratio, whereas their ionic behavior is inferred from the Cauchy pressure. Optical parameters, including the dielectric function, refractive index, extinction coefficient, reflectivity, optical conductivity, and absorption coefficient, were calculated over an energy range of 0 to 10 eV. This comprehensive study showed that these compounds have significant potential for use in optoelectronic devices.

We investigate the comprehensive analysis's structural, electronic, optical, and elastic properties of Cs₂NaScX₆ (X = Cl, Br) double perovskites using density functional theory (DFT) implemented by the WIEN2k code. The results show that both compounds are in cubic phases. The calculated tolerance factors show both are stable compounds. The computed optimized lattice parameters are Cs₂NaScX₆ (X = Cl, Br) are 10.72 Å and 12.01 Å, respectively. Employing a modified Becke–Johnson (mBJ) potential electronic nature shows that both compounds are in semiconductor nature, that is, 3.138 eV and 3.977 eV. The calculated elastic constant and perimeters show the Cs₂NaScX₆ (X = Cl, Br) are mechanical stables and also ductile and anisotropic nature. The optical properties described the range of photon energies from 0 to 10 eV, revealing pronounced absorption within the visible spectrum, highlighting their considerable promise for transformative innovations in photovoltaic technology. These double perovskites exhibit superior absorption characteristics compared to their Cs₂NaScX₆ (X = Cl, Br) analogues, thus laying the groundwork for significant advancements in solar energy conversion and photovoltaic applications.