Browsing by Author "Musembi, Robinson"

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    First-Principles Study of the Structural, Electronic, Mechanical, and Optical Properties of Zintl-Phase K2AgBi Ternary Compound for Optoelectronic Applications.
    (2025-04-23) Kachira, John Peter; Musembi, Robinson; Nyongesa, Francis; Mbilo, Mwende; Nyamuga, Martin; Musanyi, Ibrahim
    A comprehensive first-principles study was conducted to explore the structural, electronic, mechanical, thermophysical, and optical proper ties of a Zintl-phase K2AgBi ternary semiconductor compound using density functional theory. The calculations employed the local density approximation (LDA), generalized gradient approximation (GGA), and meta-GGA methods. The computed negative formation energies proved the thermodynamic stability of the K2AgBi ternary compound. The computed bandgap values were 0.6732 and 0.7848 eV for the LDA and GGA, respectively. More refined bandgap estimates were obtained using meta-GGA methods, with the Tran–Blaha modified Becke–Johnson potential yielding 0.9346 eV and the revised strongly constrained and appropriately normed functional yielding 0.9778 eV. The projected density of states study revealed that the Ag3d, Bi2p, and K1s orbitals dominate the formation of the valence band, whereas the K4p, Ag2p, and K2s orbitals contribute significantly to the formation of the conduction band. Analysis of the mechanical properties confirmed that K2AgBi is mechanically stable and ductile. Optical analysis revealed strong absorption in the 1.0–15 eV energy range, high refractive index in the low-energy region, and distinct plasmonic response, suggesting potential applications in photovoltaics, optoelectronics, and plasmonic-based technologies.
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    Insights into the Optoelectronic and Thermoelectric Properties of Lead-Free Rb2NaIrF6 Double Perovskite Compound: A First-Principles Study
    (Elsevier B.V., 2025-07-01) Mbilo,Mwende; Musembi, Robinson; Kachira, John Peter; Onsate,Wisley Nyangau; Keheze, Fanuel Mugwanga; Mapasha, Refilwe Edwin
    This study investigated the structural, electronic, elastic, mechanical, thermodynamic, optical, and thermoelectric properties of the Rb2NaIrF6 lead-free double perovskite compound using first-principles methods. The structural stability of the perovskite was confirmed by the Goldschmidt tolerance and octahedral factors. Dynamic stability was confirmed through the negative energy of formation and positive frequency modes of the phonon dispersion curve. The dynamic stability results suggest that the studied compound could be potentially synthesised experimentally. The Rb2NaIrF6 compound is a direct semiconductor with electronic band gaps within the range of 2.14-3.76 eV, computed using different approximations. The mechanical stability was confirmed by the elastic calculation results. The Rb2NaIrF6 compound was found to be ductile, ionic, and anisotropic. The optical properties showed that Rb2NaIrF6 strongly absorbs light in the ultraviolet region, which is desirable for ultraviolet-photosensitive materials in optoelectronic devices. The computed thermoelectric figure of merit of the Rb2NaIrF6 compound is 0.81 at 1000 K, suggesting high thermoelectric efficiency. These findings demonstrate the potential of Rb2NaIrF6 lead-free double perovskite compound for optoelectronic and thermoelectric applications. Therefore, our investigation offers theoretical insights that can lead to the experimental synthesis and study of Rb2NaIrF6 lead-free double perovskites.