LiMPtTl (M = Ti, Zr) Heusler alloys for high-performance energy harvesting: a DFT study.

The current study explores the electronic, thermodynamic, elastic, optical, and thermoelectric properties of the quaternary Heusler alloys LiMPtTl (M = Ti, Zr) using the full-potential linearized augmented plane wave method within the framework of density functional theory, along with semiclassical Boltzmann transport theory. Band structure and density of states calculations indicate semiconducting behavior with indirect band gaps of 0.84 eV for LiTiPtTl and 0.99 eV for LiZrPtTl. Calculations of formation energies, elastic constants, and temperature-dependent thermodynamic properties indicate structural stability, mechanical robustness, and overall stability, while also reflecting anisotropic properties. Optical spectra indicate strong dielectric behavior in the low-energy regime (~ 2 eV), followed by a gradual decrease in the higher energy range. Strong ultraviolet reflectivity indicates potential applications in UV-protective coatings, while strong optical conductivity in the visible region indicates potential applications in solar energy conversion. Transport calculations indicate an increasing power factor with temperature, indicating their potential applications in high-temperature thermoelectric devices. The lattice thermal conductivity calculated from the Slack model predicts very low values of 0.68 W m⁻¹ K⁻¹ for LiTiPtTl and 1.15 W m⁻¹ K⁻¹ for LiZrPtTl at 300 K. The Seebeck coefficients for both compounds are very high at room temperature: 1349.2 and 1890 µV K⁻¹. LiTiPtTl attains a peak figure of merit (ZT) of 0.73 at 1200 K, surpassing many reported quaternary Heusler systems in both magnitude and thermal stability. Owing to the scarcity of prior studies on these materials, these findings provide a useful platform for future theoretical and experimental exploration. This issue makes this investigation useful as future research is necessary due to a lack of previous studies.