Vanadium-Engineered Co2NiSe4 nanomaterial: coupled thermoelectric, piezoelectric, and electronic optimization via DFT+U for advanced energy applications

Abstract

The multifunctional potential of quaternary chalcogenides can be dramatically expanded by targeted pointdefect engineering. In this work, we employ density functional theory (DFT) with on-site Coulomb correction (GGA + U) to explore the structural, electronic, optical, thermoelectric, and piezoelectric properties of pristine and dilute vanadium-doped Co2NiSe4 (<= 10 at.%). Our results reveal that V substitution in monoclinic Co2NiSe4 introduces a resonant V d3 impurity level, which simultaneously (i) narrows the electronic band gap from 0.52 eV to 0.30 eV, (ii) lncrease the total spin moment from 3.2 to 3.6 mu B per formula unit, and (iii) triples the density of states at the Fermi level (Ef). These modifications lead to a significant enhancement in electrical conductivity and phonon-defect scattering, collectively boosting the thermoelectric figure of merit (zT) up to approximate to 1.1 at 900 K for 5 at.% V. Concurrently, the dielectric onset red-shifts into the near-infrared, and the dielectric constant and absorption spectrum broaden, enabling broadband light harvesting and potential NIR optoelectronic applications. The piezoelectric modulus e33 also shows a notable 23 % increase, rising to 2.70 C/m2 at 10 % V doping, indicating strong electromechanical coupling driven by lattice distortion and local symmetry breaking. Simulated X-ray absorption spectra at the Co L2,3 edges further reveal redshifted and broadened absorption peaks upon V doping, confirming enhanced Co-V hybridization and an increased unoccupied 3d-state density, which supports improved conductivity and optical response. These mutually reinforcing electronic, vibrational, and electromechanical enhancements position V-doped Co2NiSe4 as a promising multifunctional material platform for integrated heat-to-power conversion, near-infrared photodetection, and spintronic or spin-filter applications. The study highlights how targeted substitutional doping in chalcogenides can unlock simultaneous improvements across energy, sensing, and actuation domains.