Synthesis and thermoelectric properties of Mn-doped AgSbTe₂ compounds

Polycrystalline p-type Ag_0.9Sb_1.1-xMn_xTe_2.05(x=0.05, 0.10, and 0.20) compounds have been prepared by a combined process of melt-quenching and spark plasma sintering. The sample composition of Ag_0.9Sb_1.1-xMn_xTe_2.05 has been specially designed in order to achieve the doping effect by replacing part of Sb with Mn and to present the uniformly dispersed Ag₂Te phase in the matrix by adding insufficient Te, which is beneficial for optimizing the electrical transport properties and enhancing the phonon scattering effect. All the samples have the NaCl-type structure according to our X-ray powder diffraction analysis. After the treatment of spark plasma sintering, only the sample with x = 0.20 has a small amount of MnTe₂ impurities. The thermal analysis indicates that a tiny amount of Ag₂Te phase exists in all these samples. The presence of the MnTe₂ impurity with high resistance and high thermal conductivity leads to the deteriorative thermoelectric performance of the sample with x=0.20 due to the decreased electrical transport properties and the increased thermal conductivity. In contrast, the sample with x=0.10 exhibits enhanced thermoeletric properties due to the Mn-doping effect. A dimensionless thermoelectric figure of merit of 1.2 is attained for the sample with x=0.10 at 573 K, showing promising thermoelectric properties in the medium temperature range.