Band gap engineering in ruthenium-based Heusler alloys for thermoelectric applications

In this work, systematic electronic structure calculations are performed on Ru(2)TiZ alloys to examine their structural and thermoelectric related transport properties. The electronic structural properties are analyzed using the GGA and GGA+U as exchange correlational potential. The calculated lattice parameters agree very well with the existing experimental data, and the percentage of error is less than 1%. The electronic structural properties as analyzed, using the GGA exchange correlation scheme, reveal that these alloys can be semimetals. In the band structure, it is observed that ruthenium-d and titanium-d states are lying very close to the Fermi level. Hence, computations are performed again by including the Hubbard potential for d states of ruthenium and titanium. The calculated electronic structure in GGA+U reveals that all the 3 alloys are semiconductors with the indirect energy gap of 0.209, 0.175, and 0.259eV, respectively, for Ru2TiSi, Ru2TiGe, and Ru2TiSn. The electrical transport coefficients are calculated in both the GGA and GGA+U exchange correlational potential and reported. If experimentalists prove that these alloys are semiconductors, then all 3 alloys will be potential thermoelectric materials. If by experiment they are semimetals, only then Ru2TiSn can be a good thermoelectric material. Doping of electron and hole for various concentrations is studied for Ru2TiSn, and optimum doping level is reported.