2, University of California, Los Angeles, Los Angeles, California, United States
3, Michigan State University, East Lansing, Michigan, United States
The state-of-the-art thermoelectric power system for space applications has typically been based up on either Si1-xGex alloys or PbTe/TAGS for the past 50 years. Although reliable and robust, the thermoelectric performance of these systems remains low with a system level conversion efficiency of ~6%. In recent years, complex materials such as n-type La3-xTe4 and p-type Yb14MnSb11 have emerged as new high efficiency, high temperature thermoelectric materials with ZTmax on the order of 1.2 at 1275 K. The high performance of these complex structures is attributed to their favorable characteristics such as semi-metallic behavior due to small band gaps, low glass-like lattice thermal conductivity values due to structural complexity and reasonably large thermopower values near their peak operating temperatures. Computational modelling indicates that the conduction band of La3-xTe4 is dominated by the La d-orbitals. Introduction of states near the Fermi level could potentially lead to a significant enhancement of the electronic transport properties. Praseodymium telluride (Pr3-xTe4) is a La3-xTe4 analogue with 3 f-electrons (whereas La has none). Density functional theory (DFT) calculations indicate that the f-electrons lead to a sharp peak in the conduction band edge near the fermi level. In order to verify the theoretical calculations, we utilized a mechanochemical approach to synthesize Pr3-xTe4 with various Pr:Te vacancy concentrations. The powders were compacted using spark plasma sintering (SPS) and the compacts were characterized using X-ray diffraction, scanning electron microscopy, and electron microprobe analysis. The temperature dependent electrical resistivity, Seebeck coefficient, and thermal conductivity will be presented and discussed.