A Comprehensive Analysis of CoHfX (X = As, Bi) Half Heusler Alloys: Implications for High-Performance Thermoelectric and Photovoltaic Devices

The linearized full-potential augmented plane wave method within the framework of density functional theory (DFT) was employed to investigate the structural, elastic, electronic, optical and thermoelectric properties of the cobalt-based half-Heusler alloy CoHfX (X = As, Bi). The exchange-correlation functional was treated using the generalized gradient approximation of Perdew-Burke-Ernzerhof (GGA-PBE) and the Tran-Blaha-modified Becke-Johnson (TB-mBJ) approach as implemented in the WIEN2k package. The results indicate that the studied material is mechanically stable, suggesting its potential for experimental synthesis. Noteworthy findings include Debye temperatures of 317.42 K for CoHfAs and 343.26 K for CoHfBi, highlighting distinct thermal behaviors. The electronic band structures and density of states confirm the semiconductor nature of these compounds, with indirect band gaps of 1.36 eV for CoHfAs and 1.12 eV for CoHfBi, as determined using the TB-mBJ approximation. To examine the thermoelectric properties, including the Seebeck coefficient (S), electrical conductivity (σ), thermal conductivity (κ), and figure of merit (ZT), Boltzmann transport equations within the DFT framework were employed. The significant values obtained for the figure of merit and Seebeck coefficient indicate that CoHfX alloys are promising candidates for thermoelectric applications. The materials under investigation also exhibit exceptional absorption coefficients (α(ω)) in the ultraviolet and visible regions of the light spectrum, making them suitable for photovoltaic and optical equipment manufacturing. To date, no experimental or theoretical studies have been conducted on the half-Heusler alloy CoHfX. Consequently, the theoretical findings regarding the structural, elastic, electronic, magnetic, and thermoelectric properties are likely to be corroborated by future experimental investigation.