Figure of merit enhancement in thermoelectric materials based on gamma-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 gamma-Ln(0.8)Yb(0.2)S(1.5-)(y) (Ln = Gd, Dy) solid solutions. It was found that Yb3+ ions in gamma-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 gamma-Ln(0.8)Yb(0.2)S(1.5-)(y) solid solutions. The lowest electrical resistivity 20 mu ohm m at 750 K and the thermal conductivity 0.58 W/m K at 973 K, the highest Seebeck coefficient 125 mu V/K at 700 K and the maximum thermoelectric efficiency, ZT = 0.60 (at 770 K) were obtained for gamma-Dy0.8Yb0.2S1.5-y.