Despite similar chemical compositions, the CuMO2 (M = H, Li, Na, K, Rb) compounds show remarkably distinct structural, electronic, dynamical, and optical properties. Different alkali atoms have a significant influence on their electronic, dynamical, and optical behavior. By means of first principles based density functional theory calculations, we explore the universality of electronic characteristics, dynamical stability, and optical properties of these compounds. The electronic band structures, vibrational frequencies, and optical properties are deeply connected with the atomic radius of the alkali atoms. The electronic bandgap of CuMO2 (M = H, Li, Na, K, Rb) lies within the range of 0.5–1.0 eV bringing them in the group of low bandgap p-type semiconductors. We found a significant increase in the bandgap and p–d hybridization as going from H to Rb. Partial density of states revealed strong metal–oxygen (Cu–O) overlap due to the strong p–d hybridization. The phonon dispersion curves obtained for these compounds confirm the dynamical stability as there is no imaginary frequency throughout the Brillouin zone. The static dielectric constants and refractive index fall within the range of 8.0–12.91 and 1.98–3.55, respectively, suggesting the usefulness of scrutinized compounds in non-linear optical devices. The optical properties depict that the alkali atoms based delafossites can serve as promising candidates for highly efficient optical devices within a broad range from visible to ultraviolet light of electromagnetic spectra.
The ternary chalcopyrite compounds and related structures are well known for their noteworthy electronic and optical properties. The interaction between monovalent and trivalent atoms has a significant influence on their electronic as well as optical behavior. In the present work, a density functional theory based first-principles calculation is performed to investigate the structural, electronic, lattice dynamical, and optical properties of rhombohedral CuRhX2 (X = S, Se, Te) compounds. The electronic band structure of these compounds depicts semiconducting nature with an indirect bandgap of 1.8, 1.17, and 0.75 eV for CuRhS2, CuRhSe2, and CuRhTe2, respectively. There is a greater hole mobility and p-type conductivity in these compounds due to strong p-d hybridization. The phonon dispersion curves of these compounds confirm their dynamical stability as there is no imaginary frequency for any of the phonon modes in the entire Brillouin zone (BZ). Furthermore, we discuss mode compatibility at the zone center of the BZ and other high symmetry points of the BZ. The Raman spectra of CuRhX2 demonstrate two Raman active modes, namely, the Eg and A1g. The frequency of Raman active modes Eg and A1g decreases due to the increase in Rh–X bond length. The static dielectric constants fall in the range of 8.7–10.4. The absorption coefficient of these compounds is in the range of 1.5–2.0 eV depending upon the ionic radii of chalcogen atoms. Thus, it can be deduced that these systems can be efficiently used in solar energy converters in the UV as well as in the visible region.
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