Thermodynamic and thermoelectric properties of CoFeYGe (Y = Ti, Cr) quaternary Heusler alloys: first principle calculations.

Utilizing a material in thermoelectric applications requires a mechanical, thermal, and lattice stability as well a high figure of merit (ZT). In this work, we present the structural, electronic, magnetic, mechanical, thermodynamic, dynamic, and thermoelectric properties of CoFeYGe (Y  =  Ti, Cr) quaternary Heusler compounds using the density functional theory (DFT). The calculated mechanical properties and phonon dispersions reveal that the structures of these compounds are stable. Both CoFeCrGe and CoFeTiGe compounds show a ferromagnetic and ferrimagnetic half-metallic behavior with band gaps of 0.412 and 0.383 eV, respectively. The lattice thermal conductivity (κ L) exhibits low values that reach 3.89 W (m · K)-1 and (4.48 W (m · K)-1) for CoFeCrGe (CoFeTiGe) at 850 K. The optical phonon modes have a large contribution of 60.2% (70.9%) to κ L value for CoFeCrGe (CoFeTiGe). High ZT values of 0.64 and 0.57 were obtained for CoFeCrGe and CoFeTiGe, respectively. Based on our calculations, CoFeCrGe and CoFeTiGe combine both good spintronic and thermoelectric behaviors that may be used in spin injection applications.