SrFBiS₂ is a quaternary n-type semiconductor with rock-salt-type BiS₂ and fluorite-type SrF layers alternately stacked along the c axis. The tunability of the crystal and electronic structures as well as the intrinsically low thermal conductivity make this compound a promising parent material for thermoelectric applications. In the current work, we show that alloying of Se and S in SrFBiS₂ reduces the optical band gap with the second conduction band serving as an electron-transport medium, simultaneously increasing the electron concentration and effective mass. In addition, the raw material Bi₂Se₃ is shown to act as liquid adjuvant during the annealing process, favoring preferred-orientation grain growth and forming strengthen microstructural texturing in bulk samples after hot-pressed sintering. Highly ordered lamellar grains are stacked perpendicular to the pressure direction, leading to enhanced mobility along this direction. The synthetic effect results in a maximum power factor of 5.58 μW cm⁻¹ K⁻² at 523 K for SrFBiSSe and a peak zT = 0.34 at 773 K, enhancements of 180% compared with those of pristine SrFBiS₂.

The quaternary diamond-like compounds, A₂Cu₃In₃Te₈ (A = Cd, Zn, Mn, Mg), are a new class of thermoelectric materials recently proposed by complex structure design. Among them, the Zn₂Cu₃In₃Te₈ compound possesses reasonable electrical transport properties but relatively high lattice thermal conductivity. Herein, the effects of Ag substitution on the phase stability and thermoelectric properties of Zn₂Cu₃In₃Te₈ compound are reported. It is revealed that only the In sites show an appreciable tolerance for Ag doping. Ag substitution at the In sites introduces extra holes and thus results in improved electrical transport properties. Furthermore, the introducing of Ag lowers the sound velocities and enhances the phonon scattering of the Zn₂Cu₃In₃Te₈ compound, which leads to a substantially reduction in lattice thermal conductivity. Finally, in virtue of the optimization in both electrical and thermal transport properties, the maximal zT value of Zn₂Cu₃In_2.8Ag_0.2Te₈ sample reaches 0.62 at 823 K, which is 43% higher than the pristine sample.