Daniel Thompson

High Seebeck coefficient AMXP2 (A = Ca and Yb; M, X = Zn, Cu and Mn) Zintl phosphides as high-temperature thermoelectric materials

Resistivity (?), Seebeck coefficient (?) and thermal diffusivity of the title compounds CaZn2P2, YbZn2P2, YbCuZnP2 and YbMnCuP2 are measured over a temperature range 300?1000?K to evaluate the thermoelectric potential of these materials. The temperature dependence of ? and ? of these light weight and less explored Zintl phosphides is similar to that of a degenerate semiconductor. While the electrical transport properties ? and ? are strongly composition dependent, thermal conductivity (?) calculated from thermal diffusivity is remarkably low in the range 1.1?2.5?W?m?1?K?1 at 1000?K. Room-temperature Hall resistance measured on selected samples suggests that holes dominate in the transport. The best composition appears to be YbZnCuP2 which has the combination of ? ~ 2.4?m??cm, ? ~ 160??V?K?1 and ? ~ 1.7?W?m?1?K?1 at 1000?K resulting in a ZT value of ~0.6.

New Directions in Bulk Thermoelectric Materials Research: Synthesis of Nanoscale Precursors for “Bulk-Composite” Thermoelectric Materials

Over a decade ago it was predicted that nano-scaled thermoelectric (TE) materials might have superior properties to that of their bulk counterparts. Subsequently, a significant increase in the figure of merit, ZT (ZT > 2), has been reported for nano-scaled systems such as superlattice and quantum dot systems constituently based on those more commonly used bulk TE materials (e.g., Bi 2 Te 3 and PbTe). However, the challenge remains to achieve these higher performance results in bulk materials in order to more rapidly incorporate them into standard TE devices. Recent theoretical work on boundary scattering of phonons in amorphous materials indicates that micron and submicron grains could be very beneficial in order to lower the lattice thermal conductivity and yet not deteriorate the electron mobility. The focus in this paper will be to highlight some of our new directions in bulk thermoelectric materials research. Thermoelectric materials are inherently difficult to characterize and these difficulties are magnified at high temperatures. Specific materials will be discussed, especially those bulk materials that exhibit favorable properties for potential high temperature power generation capabilities. One potentially fruitful research direction is to explore whether hybrid TE materials possess possible enhanced TE properties. These “engineered” hybrids include materials that exhibit sizes from on the order of a few nanometers to hundreds of nanometers of the initial materials. These initial materials are then incorporated into a bulk structure. A discussion of some of the future research directions that we are pursuing is highlighted, including some bulk materials, which are based on nano-scaled or hybrid composites. The synthesis techniques and the synthesis results of many of these nano-scale precursor materials will be a primary focus of this paper.