Thermoelectric properties of Tl10−xLnxTe6, with Ln = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho and Er, and 0.25 ⩽ x ⩽ 1.32

► The thermoelectric properties of Tl10−xLnxTe6 were determined. ► For each Ln, the Seebeck coefficient increases with increasing Ln amount. ► For each Ln, the electrical conductivity decreases with increasing Ln amount. ► For each Ln, the thermal conductivity decreases with increasing Ln amount. ► The lattice thermal conductivity is always very low.