Predictive modelling of multi-functional properties in XCuSO (X = Nd, Pr) oxychalcogenides via an ab initio approach

This first-principles GGA+U study thoroughly examines the electronic, optical, elastic, and thermoelectric nature of NdCuSO and PrCuSO rare-earth oxychalcogenides. Structural optimizations confirm thermodynamic stability having negative formation energy values of -3.24 eV f.u.^-1 and -3.46 eV f.u.^-1, and cohesive energies of -4.21 eV f.u.^-1 and -4.63 eV f.u.^-1 for NdCuSO and PrCuSO, respectively. Electronic band structures demonstrate intrinsic half-metallicity, with the spin-up case being metallic with the Fermi level crossing the conduction band, while the spin-down case shows semiconductor nature with energy gap values of ∼1.2 eV (NdCuSO) and ∼1.0 eV (PrCuSO), leading to approximately 100% spin polarization. The density of states study revealed dominating Cu-3d states at the valence band edge, and Nd/Pr-4f states ranging from 2-4 eV in the conduction band, and deep O-2p/S-3p bonding states, confirming significant orbital-resolved hybridization and magnetic asymmetry. Elastic constants satisfy the criteria of mechanical stability, with medium-stiffness (B = 87.8-91.7 GPa, Y = 118-126 GPa), ductile behaviour (B/G 1.9 with positive Cauchy pressure), and high elastic anisotropy (A = 0.91-0.95). Optical spectra were displayed showing high static dielectric constants, strong interband transitions at less than 2 eV, low visible reflectivity (less than 0.3), noticeable UV absorption at 7-12 eV, and plasmon resonances at 15-18 eV, showing their suitability for the optoelectronics technologies and UV-photonic. Between 300-500 K, the conduction of n-type was predicted because of the decrease in Seebeck coefficients between -6.5 to -9.2 µV K^-1 in NdCuSO, and -7.2 to -10.3 µV K^-1 in PrCuSO material. The ZT rises to 0.48 and 0.41, driven by greater electrical conductivity along with lower thermal conductivity in NdCuSO material.