Magneto-electronic, thermoelectric, thermodynamic and optical properties of rare earth YCoTiX (X = Al, Ga, Si, Ge) alloys

Abstract

The rare earth elements are extensively incorporated in combination with alloys to fill up the demanding gaps of applications in future technologies like thermoelectrics. We give detailed prediction of electronic, magnetic, mechanical, thermoelectric, thermodynamic and optical properties of YCoTiX (X = Al, Ga, Si, Ge) quaternary Heusler alloys. The ground state properties reveal the alloys possess the LiMgPdSn-type structure with F-43m space group. The spin polarized band structure give us a half-metallic nature at optimized lattice parameters. The minority spin band gaps are found to be indirect with calculated values as 0.53 eV for YCoTiAl, 0.61 eV for YCoTiGa, 0.71 eV and 0.62 eV for YCoTiSi and YCoTiGe, respectively. The total magnetic moment follow the Slater-Pauling curve rule of (M = Ztot – 18). Similarly, the optical properties of these alloys depict the similar behavior of electronic states near the Fermi level with substantially spins oriented along the direction of magnetization in all the alloys. The thermoelectric coefficients are investigated to infer their stand for waste heat recovery systems, where Seebeck coefficients detail their n-type behavior. Conversion efficiency is established using the dimensionless figure of merit, zT calculated as 0.75 at 550 K for YCoTiAl, 0.14 at 750 K for YCoTiGa and 0.31 at 750 K for both YCoTiSi (Ge). Thermodynamic parameters convey that all the alloys possess no anomalies with respect to phase transition or instabilities.