Good thermoelectric materials possess low thermal conductivity while maximizing electric carrier transport. This article looks at various classes of materials to understand their behavior and determine methods to modify or “tune” them to optimize their thermoelectric properties. Whether it is the use of “rattlers” in cage structures such as skutterudites, or mixed-lattice atoms such as the complex half-Heusler alloys, the ability to manipulate the thermal conductivity of a material is essential in optimizing its properties for thermoelectric applications.
Half-Heusler (HH) alloys have attracted considerable interest as promising thermoelectric (TE) materials in the temperature range around 700 K and above, which is close to the temperature range of most industrial waste heat sources. The past few years have seen nanostructuing play an important role in significantly enhancing the TE performance of several HH alloys. In this article, we briefly review the recent progress and advances in these HH nanocomposites. We begin by presenting the structure of HH alloys and the different strategies that have been utilized for improving the TE properties of HH alloys. Next, we review the details of HH nanocomposites as obtained by different techniques. Finally, the review closes by highlighting several promising strategies for further research directions in these very promising TE materials.
We experimentally investigate the electron and phonon contributions to the thermal conductivity of amorphous GdFeCo and TbFeCo thin films. These amorphous rare-earth transition-metal (RE-TM) alloys exhibit thermal conductivities that increase nearly linearly with temperature from 90 to 375 K. Electrical resistivity measurements show that this trend is due to an increase in the electron thermal conductivity over this temperature range and a relatively constant phonon contribution to thermal conductivity. We find that at low temperatures ($90 K), the phonon systems in these amorphous RE-TM alloys contribute $70% to thermal conduction with a decreasing contribution as temperature is increased. V
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