Theoretical Insights into the Electronic, Optical, Mechanical, and Thermoelectric Characteristics of Double Half-Heusler Nb ₂ Sn ₂ OsZ (Z = Pd, Pt)

This study presents a first-principles investigation of the structural, electronic, optical, elastic and thermoelectric properties of Nb 2 Sn 2 OsZ (Z = Pd or Pt). Structural optimization confirms that both compounds crystallize in the tetragonal I-42d phase and satisfy the Born-Huang mechanical stability criteria. Electronic calculations reveal indirect gaps of approximately 0.5 eV, classifying the compounds as small-gap semiconductors with strong d-p hybridization, which is indicative of covalent bonding and favorable electrical conductivity. The optical properties demonstrate strong absorption in the visible range (1-3 eV), high refractive indices and plasmon peaks near 32 eV, suggesting potential applications in optoelectronics. Elastic analysis indicates ductile behavior (B/G ≈ 2.0, σ ≈ 0.29) with moderate anisotropy, supporting mechanical durability. The thermoelectric results reveal temperature-enhanced Seebeck coefficients and power factors, with maximum figures of merit of ~0.70 for Nb 2 Sn 2 OsPd and ~0.77 for Nb 2 Sn 2 OsPt at 1200 K, indicating strong potential for energy conversion and electronic devices.