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Intercalation of large organic spacer cations with inorganic layers of octahedral metal halide cages in 2D-Ruddlesden–Popper (RP) monolayer perovskites (R–NH3) 2 A n −1 B n X 3n+1 by using a rational design approach has shown structural versatility and energetic stability. A systematic theoretical investigation of the structural, electronic, and mechanical properties was conducted with and without spin-orbit coupling (SOC) under the influence of a range of organic monovalent spacer cations [R–NH 3 ] + with different inorganic halide anions. This resulted in 12 compositions. Lattice distortion and octahedral tilting provided gradient band gaps that displayed a good linear relationship with equatorial Sn–X–Sn angles in debt of larger halide anions. By fixing halide ions, larger spacer cations reduce the band gap further. The halides function as acceptors, whereas Sn and N function as donors. Intermingled N -atoms of spacer cations incorporate additional charges to axial halide ions of [SnX 6 ] 4- with state-of-the-art features of defect tolerance, quantum and dielectric confinement, low effective masses, and high mobility. Graphical representation of compositionally modified 2D-Ruddlesden – Popper (RP) monolayer perovskites (R–NH 3) 2 An −1 B n X 3n+1 configured into 12 structures by systematically substituting the inorganic anions (X = Cl, Br, I) in [SnX 6 ]4- octahedra and monovalent organic spacer cations [R–NH 3 ]+, including butyl-ammonium (C 8 H 24 N 2), hexyl-ammonium (C 12 H 32 N 2), phenyl-ammonium (C 16 H 24 N 2), and octyl-ammonium (C 16 H 40 N 2). [Display omitted] • Density functional theory (DFT) validates experimentally designed structures. • New 2D semiconductor perovskites are designed with appropriate band gaps closer to the optimal band gap of solar cells. • The degree of structural stability of 2D-perovskites gets improved with smaller spacer cations and halide anions. • The band gap of 2D-perovskites gets reduced in the order of larger A-cations and X-halide anions. • The octahedral tilting by varied halide anions and lattice compression by spacer cations tune the properties. [ABSTRACT FROM AUTHOR]

Half-Heusler (HH) alloys are a well-known and extensively researched family of thermoelectric (TE), magnetic, and spintronic materials. Doping may significantly increase the thermoelectric conversion efficiency of these materials; nevertheless, practical applications remain far. As a result, the hunt for superior parent TE alloys is critical. Using extensive first-principles density functional calculations, we predicted a novel class of vanadium-based four HH VXTe alloys, where X is one of the four elements: Cr, Mn, Fe, and Co. Their TE properties, as well as their mechanical, magnetic, electrical, and structural stability, have been studied in depth. Their mechanical and thermodynamic stability is confirmed using the predicted elastic constants, formation and cohesive energies, and phonon spectra. A comprehensive analysis of elastic constants and moduli demonstrates that HH VXTe alloys possess elastic anisotropy with reasonably good machinability, higher melting and Debye temperatures, mixed bonding characteristics with ionic and covalent contributions, and brittle nature, except for VCoTe, which is ductile. We find that the ground state of HH VCrTe and VFeTe is ferrimagnetic, while HH VCoTe is ferromagnetic and HH VMnTe is non-magnetic. Three VXTe (X = Cr, Fe, & Co) alloys demonstrated half-metallicity with 100% spin-polarization, whereas HH VMnTe is an 18-electron indirect semiconductor. In the studied HH VXTe alloys, most of the heat flow is caused by the phonon-group velocity of the acoustic phonons. Further studies on the relationship between carrier concentration and temperature dependence of TE properties reveal that the high ZT ∼1.2 at 1000 K of the pristine HH VMnTe alloy is obtained due to its high-power factor of 249.4 × 10 12 W m − 1 K − 2 and this value is greater than the values of some known pristine and doped HH TE materials. Our findings pave the way for further investigation into the HH VXTe alloys in the quest for improved TE and spintronic materials for use in domains that necessitate high thermoelectricity and spintronic performance. [ABSTRACT FROM AUTHOR]