Thermoelectric properties of Cu4Ge3Se5 with an intrinsic disordered zinc blende structure

Abstract

The development of novel thermoelectrics has largely relied on the discovery of materials with a low lattice thermal conductivity. Disordered point defects have been demonstrated to be effective in reducing the lattice thermal conductivity through the resultant strong phonon scattering. In this work, ternary zinc blende Cu_4−δGe₃Se₅, intrinsically coming with a high degree of intrinsic atomic disorder, is focused on, with an expectation of a low intrinsic lattice thermal conductivity for potential thermoelectric applications. The so-called Cu₄Ge₃Se₅ compound is found to be stabilized at a Cu-deficient composition of around Cu_3.5Ge₃Se₅ and the lattice thermal conductivity (κ_L) is revealed to be only 0.6 W m⁻¹ K⁻¹ at 750 K, which is about one order of magnitude lower than that of ordered binary zinc blende compounds (including group III–V and IIB–VI compounds). This ensures a peak zT of 0.5 to be achieved at 750 K, which is competitive to that of single-crystal InSb. In addition, a single parabolic band (SPB) model with acoustic phonon scattering provides a reasonable understanding of the electronic transport properties. This work illustrates the strategy of intrinsic atomic disorder for novel thermoelectrics with a low lattice thermal conductivity.