First-principles calculations to investigate structural, electronic, mechanical, and optical properties of double half-Heusler alloys YNbPd2Sn2, and YNbPt2Sn2

Due to their tunable electronic structure and low thermal conductivity, double half-Heusler (DHH) alloys have garnered considerable attention as promising candidates for optoelectronic and multifunctional applications. In this research, two novel double half-Heusler compounds, YNbX 2 Sn 2 (X = Pd, Pt), have been introduced, and a detailed analysis of their structural, electronic, mechanical, optical, and thermodynamic properties has been presented using density functional theory for the first time. Negative formation energies (E F ) confirm thermodynamic stability, the absence of imaginary phonon modes confirms dynamical stability. Electronic band structure (hybrid HSE06 for accurate gap prediction) exhibit an indirect semiconductor bandgap of 0.56 eV and 1.03 eV, respectively. Mechanical properties have been thoroughly evaluated by calculating elastic constants ( C ij ) satisfy the Born criteria, elastic moduli, fracture toughness, machinability, and Vickers hardness; calculated Pugh’s and Poisson’s ratios further demonstrate ductility. The frequency-dependent optical functions absorption coefficients, high optical conductivity, and high reflectivity show pronounced peaks across the infrared (IR) to ultraviolet (UV) regions along with XX, YY and ZZ direction. Thermal properties—Debye temperature, Grüneisen parameter, lattice thermal conductivity (Slack model), minimum thermal conductivity, specific heats and thermal expansion—have been evaluated from 0 to 1000 K. At 300 K, each compound exhibits a low lattice thermal conductivity K ph (4.40–4.69 Wm −1 K −1 ), which makes them reliable for multifunctional device performance under elevated temperatures and efficient heat management applications.