Figure of merit enhancement in thermoelectric materials based on γ‐Ln _0.8 Yb _0.2 S _{1.5‐ y} (Ln = Gd, Dy) solid solutions

Here we report the study temperature dependencies of the Seebeck coefficient, the electrical resistivity ( T = 300–750 K), the total thermal conductivity ( T = 300–973 K), and the thermoelectric figure of merit ( T = 300–750 K) of ceramic samples of γ‐Ln 0.8 Yb 0.2 S 1.5‐ y (Ln = Gd, Dy) solid solutions. It was found that Yb 3+ ions in γ‐Ln 0.8 Yb 0.2 S 1.5‐ y act as the promoters of higher crystallite nucleation rate during the formation of solid solutions. This results in the sample dispersion increase and the formation of the additional phonon scattering centers (dislocations and strain stresses along the crystallites semi‐coherent boundaries). These features of the real structure determined the low value of thermal conductivity of γ‐Ln 0.8 Yb 0.2 S 1.5‐ y solid solutions. The lowest electrical resistivity 20 μΩ m at 750 K and the thermal conductivity 0.58 W/m K at 973 K, the highest Seebeck coefficient 125 μV/K at 700 K and the maximum thermoelectric efficiency, ZT = 0.60 (at 770 K) were obtained for γ‐Dy 0.8 Yb 0.2 S 1.5‐ y .