Prediction of the electronic structure, optical and vibrational properties of ScXCo2Sb2 (X = V, Nb and Ta) double half-Heusler alloys: a theoretical study

Our calculations allowing to establish a link between atomic topology and properties, based on the interpretation of the electronic structure. ScXCo2Sb2 (X = V, Nb and Ta) double half-Heusler alloys (DHH) are nonmagnetic materials. Based on an ab initio study these materials is found to be semiconductors with an indirect band gap in the range 0.56-0.81 eV. Our DFT calculations confirm that the band gap increasing upon the replacement of V by Nb by Ta atoms. In all compounds Co-d orbitals are locating close to the Fermi level and a hybridization of Co-d, X-d and Sc-d bands lies above the Fermi level. More precisely, the optical properties have been calculated and discussed. The photon energy dependence of the dielectric function and optical conductivity is determined from 0 up to 20 eV. Prominent absorptions are observed in these compounds in the energy region of 2-4.0 eV due to interband optical transitions. The reflectivity spectra and the refraction index are also calculated and discussed. The structural stability of ScXCo2Sb2 (X = V, Nb and Ta) DHH has been confirmed by elastic constants calculations. The atomic bonds between nearest neighbors along (100) planes are weaker than those along (001) planes. However, for ScVCo2Sb2, the atomic bonds are weaker along (001). The studied materials are found to be somewhat hard compounds, elastically stable and have a brittle character except ScVCo2Sb2 compound. The positive frequencies in the phonon dispersions of ScXCo2Sb2 (X = V, Nb, Ta) DHH, indicating that they are dynamically stable.