Study on the effect of Pb partial substitution for Te on the thermoelectric properties of La3Te4-xPbx materials

The effect of Pb in La3Te4-xPbx on the thermoelectric properties in the temperature range 300-1100 K was studied on samples synthesized by the melting, ball milling and hot-pressing method. The samples crystallize in the Th(3)P(4)structure. A small amount of Pb substitution for Te in La3Te4 reduced the electrical conductivity, but the impurity phase introduced by more Pb significantly enhanced the electrical conductivity. The electrical conductivity of the La3Te3.6Pb0.4 sample reached 2.06 x 10(5) S m(-1) at room temperature. The expansion of crystal lattice confirmed from x-ray diffraction patterns and the slight reduction in electrical conductivity all verify the fact that Pb substitutes a Te site when x is small. The Seebeck coefficient increases linearly with temperature for all samples. While the thermal conductivity varies slightly with temperature, the lattice thermal conductivity approaches the minimum value at high temperatures. For La3Te3.7Pb0.3, a power factor of 1.4 x 10(-3) W m(-1) K-2 at 1100 K was achieved with a thermal conductivity of 1.86 W m(-1) K-1, giving a maximum figure-of-merit ZT approximate to 0.8 at 1100 K.