First principle study of structural, electronic, optical, and thermoelectric properties of Zr1-xMxNiSn (M = Ta, Nb and x=0.25, 0.5, 0.75) half Heusler compounds: Green energy applications

In the present paper, the physical properties of doped Zr1-x MxNiSn (M = Ta, Nb and x = 0.25, 0.5, 0.75) half Heusler compound were investigated using density functional theory (DFT) with GGA-PBE and Tran-Blaha modified Becke-Johnson (TB-mBJ) exchange potentials. The Full Potential Linearized Augmented Plane Wave (FP-LAPW) technique was used as incorporated in the WIEN2k code. The band structures, as well as the density of states (DOS), are also studied. The lattice constants of 6.15 angstrom for pure and 6.12 angstrom reinforced compounds are obtained. The results show that pure alloys are semiconducting, and doped alloys are metallic. The elastic properties were also examined, and the results indicate that the compounds are mechanically stable. The optical properties such as absorption coefficient (I), optical conductivity (sigma), electron energy-loss (L), refractive index (n), and extinction coefficient (K) were determined using the dielectric constants (epsilon). The optical results revealed that the materials are potential candidates for optoelectronic energy applications. The transport properties were also studied. The doping of Ta and Nb in ZrNiSn alloy increases the electrical conductivity in both GGA-PBE and TB-mBJ approaches. The electrical conductivity for pure ZrNiSn at room temperature is 4.67 x 10(18) Omega(-1)m(-1)s(-1) and it increases to 4.34 x 10(20) Omega(-1)m(-1)s(-1) for Zr0.5Ta0.5NiSn in GGA-PBE approach. The thermal conductivity's electrical component is increased by substituting Ta and Nb in the pure compound. The optical and thermoelectric properties make the materials a suitable candidate for green energy applications.