A First-Principles Investigation on the Structural, Optoelectronic, and Thermoelectric Properties of Pyrochlore Oxides (La₂Tm₂O₇ (Tm = Hf, Zr)) for Energy Applications

A first-principles calculation based on DFT investigations on the structural, optoelectronic, and thermoelectric characteristics of the newly designed pyrochlore oxides La2Tm2O7 (Tm = Hf, Zr) is presented in this study. The main quest of the researchers working in the field of renewable energy is to manufacture suitable materials for commercial applications such as thermoelectric and optoelectronic devices. From the calculated structural properties, it is evident that La2Hf2O7 is more stable compared to La2Zr2O7. La2Hf2O7 and La2Zr2O7 are direct bandgap materials having energy bandgaps of 4.45 and 4.40 eV, respectively. No evidence regarding magnetic moment is obtained from the spectra of TDOS, as a similar overall profile for both spin channels can be noted. In the spectra of ε2(ω), it is evident that these materials absorb maximum photons in the UV region and are potential candidates for photovoltaic device applications. La2Tm2O7 (Tm = Hf, Zr) are also promising candidates for thermoelectric device applications, as these p-type materials possess ZT values of approximately 1, which is the primary criterion for efficient thermoelectric materials

Spin-Dependent First-Principles Study on Optoelectronic Properties of Neodymium Zirconates Pyrochlores Nd₂Zr₂O₇ in Fd-3m and Pmma Phases

Rare-earth zirconate pyrochlores (RE2Zr2O7) are of much fundamental and technological interest as optoelectronic, scintillator and thermal barrier coating materials. For the first time, we report the detailed optoelectronic properties of rare-earth zirconates Nd2Zr2O7 in both, i.e., for spin up and spin down states, via the use of first-principles density functional theory (DFT) procedure. To obtain the desired optoelectronic properties, we used a highly accurate method called full-potential linearized augmented plane wave (FPLAPW) within the generalized gradient approximation (GGA), parametrized with Hubbard potential U as an exchange-correlation function. The band gaps predicted for Nd2Zr2O7 were of the order 2.4 eV and 2.5 eV in Fd-3m and Pmma symmetrical phases, respectively. For both the phases, our research involved a complete examination of the optical properties of Nd2Zr2O7, including extinction coefficient, absorption coefficient, energy loss, function, reflectivity, refractive index, and real optical conductivity, analyzed in the spectral range from 0.0 eV to 14 eV. The calculated optical properties in both phases showed a considerable spin-dependent effect. The electronic bonding characteristics of different species in Nd2Zr2O7 within the two crystal symmetries were explored via the density distribution mapping of charge

Optoelectronic properties of Nd3+ doped CaTa2O6: Insights from the GGA plus U calculations

The current work is a study of optoelectronic properties of Nd3+ doped CaTa2O6 using the FP-LAPW (full potential-linear augmented plane wave) method as implemented within the WIEN-2k code. The GGA (generalized gradient approximation) has been used as E-XC (exchange-correlation) functional for the calculations of electronic and optical properties with Hubbard correction. The optimized crystal structure shows close agreement with experimental results. In order to ensure the accuracy of the electronic band structure and optoelectronic properties, we have used the effective Hubbard parameter "U" for the 4f-electrons of the Nd atom. Electronic band structure study shows the semiconducting nature with a direct band gap. The VBM (valance band maximum) and CBM (conduction band minimum) are located at the Gamma-point of the Brillouin zone. Optical properties were studied by taking into account the interband transitions. A number of optical transition levels have been found. We have evaluated various optical constants, like the absorption coefficient, reflectivity, energy loss function and refractive index as function of incident photon energy. Both band structure and optical parameters have been investigated for up and down electron spin configurations. Nd3+ doped CaTa2O6 possesses high degree of spin symmetry, except at low energy, and absorbs ultraviolet photons strongly and weakly reflects photons in the infrared and visible energies. These optical characteristics can be useful for optoelectronic device applications

Vliv S a Se výměně na elektronických a termoelektrických vlastností BaCu2GeQ4 (Q = S, Se) chalkogenidových krystalů

Pro kvartérního chalkogenidy BaCu2GeQ4 (Q = S, Se), optoelektronických, strukturální a transportní vlastnosti jsou zkoumány pomocí přesné všechny elektrony FPeLAPW metoda [plný potenciál linearizován rozšířený rovinné vlny]. Mřížkové konstanty vypočtené teoreticky jsou stanovena tak, aby v dobré shodě s hodnotami, které jsou měřeny experimentálně. Je zjištěno, že všechny Titulní sloučeniny jsou přímé polovodiče zakázaným pásem, a tato energie odstupu pásma se nachází G-G symetrie bodů. Současně se při výměně S pomocí SE zakázaný pás velikost se snižuje. Optické konstanty disperze jako imaginární a reálné složky dielektrických funkcí, extinkčních koeficientů, indexu lomu, odrazivost je, absorpčních koeficientů, které byly také vypočteny pro tyto sloučeniny. Vysoká absorpce a přímé charakteristiky zakázaným pásem těchto sloučenin v UVeVisible energetickém rozsahu ukazují, že tyto perovskytové struktury by mohly být použity v optoelektronických a optických přístrojů pracujících v UV eVisible rozsahu energetického spektra. Vypočtený dvojlom (0,012 a 0,083) zvyšuje vhodnost BaCu2GeSe4 srovnání s BaCu2GeS4 obvykle aplikuje jako nelineární optické materiály. Vypočtené dopravy koeficienty vykazují anizotropní charakter materiálů, po dohodě s jejich elektronových stavů. Transportní vlastnosti ukazují silnější koncentrace nosiče podél Ge-s, Ba-P a Cu-d orbitalů, což potvrzuje, že tyto orbitaly jsou hlavní pro elektrické dopravní funkce. Hodnoty efektivní hmotnosti elektronů jsou vypočteny podle zakřivení CBM pásma 124 a 184 pro BaCu2GeS4 a BaCu2GeSe4 resp. Zkoumání termoelektrického účiníku ukazuje, že BaCu2GeS4 je mnohem lepší než BaCu2GeSe4 v celém teplotním intervalu, který dělat to vhodný pro budoucí technologické aplikaceFor the Quaternary Chalcogenides BaCu2GeQ4 (Q ¼ S, Se) optoelectronic, structural and transport properties are explored using accurate all electrons FPeLAPW [full potential linearized augmented plane wave] method. The lattice constants calculated theoretically are established to be in fine agreement with the values that are measured experimentally. It is established that all the titled compounds are direct band gap semiconductors and this energy band gap is situated G- G symmetry points. At the same time the band gap magnitude decreases during replacement of S by Se. Optical constant dispersion like imaginary and real components of dielectric functions, extinction coefficients, refractive indices, reflectivity's, absorption coefficients, have been also calculated for these compounds. High absorption and the direct band gap characteristics of these compounds in the UV-Visible energy range indicate that these perovskite structures might be used in optoelectronic and optical devices working in the UV-Visible range of the energy spectrum. The calculated birefringence (0.012 and 0.083) enhances the suitability of BaCu2GeSe4 compared to BaCu2GeS4 usually applied as nonlinear optical materials. The computed transport coefficients exhibit the anisotropic nature of the materials, in agreement with their electronic states. The transport properties show stronger carrier concentrations along the Ge-s, Ba-p and Cu-d orbitals, confirming that these orbitals are principal for the electrical transport features. The values of effective mass of electrons are computed by curvature of the CBM band 124 and 184 for BaCu2GeS4 and BaCu2GeSe4 respectively. Investigating of the thermoelectric power factor shows that BaCu2GeS4 is much better than BaCu2GeSe4 over the entire temperature interval which make it suitable for future technological application