Phonon phase stability, structural, mechanical, electronic, and thermoelectric properties of two new semiconducting quaternary Heusler alloys CoCuZrZ (Z = Ge and Sn)

For meeting the energy demand, the development of new and novel thermoelectric (TE) materials for power generation is very vital. In this draft, we have theoretically investigated two new quaternary CoCuZrZ (Z = Ge and Sn) Heusler alloys for their structural, mechanical, electronic, and TE properties. In the energy minimization process, the alloys are found to be non-magnetic in the ground state. Based on calculated phonon dispersion curves, formation energy, and elastic constants, we propose that both CoCuZrGe and CoCuZrSn are stable. Furthermore, the mechanical properties indicate that CoCuZrGe (CoCuZrSn) has a brittle (ductile) nature. The electronic properties examined in Perdew-Burke-Ernzerhof (PBE), PBEsol, and modified Becke-Johnson (mBJ) potential, all predict that reported systems are narrow-gap semiconductors (SCs). In addition, the temperature dependent TE properties have been studied by calculating the electronic thermal conductivity (kappa), Seebeck coefficient (S), power factor (PF) and electrical conductivity (sigma/tau). The obtained positive value of S conveys the materials as p-type SCs, with a maximum value of 26.2 mu V/K for CoCuZrGe and 28 mu V/K for CoCuZrSn. The sigma/tau, kappa, and PF show increasing trends with rising temperature. The PF is found to be 1.55 x 10(12) WK(-2)m(-1)s(-1) for CoCuZrGe and 1.38 x 10(12) WK(-2)m(-1)s(-1) for CoCuZrSn. The proposed semiconducting Heusler alloys may receive attention for a range of TE and spintronic applications.