Combined Experimental and First Principles Study on Nanostructured NbFeSb Half-Heusler Alloy Synthesized by Mechanical Alloying

The Half-Heusler semiconductor alloys can be used efficiently as thermoelectric materials to transform the waste heat into useful electrical energy. The low-cost and large-scale production of suitable half-Heusler alloys are important in the present context. In this work, a nanostructured half-Heusler NbFeSb alloy is obtained by mechanical alloying with 15h of milling. The structural parameters of the sample are investigated by powder X-ray diffraction followed by Rietveld refinement. Differential scanning calorimetry indicates that the NbFeSb phase is stable up to about 420 K. The electrical resistivity is obtained as a function of temperature. A band gap of 0.37(3) eV is obtained from UV-Vis measurements. Density functional theory calculation shows an indirect band gap of 0.52 eV. Analyses of the obtained data indicate that structural defects and nanometric crystallites sizes present in the nanostructured NbFeSb produced by mechanical alloying do not degrade the electrical and optical properties of the compound.