Earth Abundant High Temperature Materials for Radioisotope Power Conversion System
Advances in high temperature thermoelectric materials were made and published. Two major developments are out lined in this final report. Alkaline earth Zintl phases represent the starting point of a series of compounds selected for development due to their high abundance as the supply chain and as the availability of certain rare earths (i.e. Yb) are limited and can be difficult to obtain. A new Zintl phase, Ca14MnSb11-xSnx, where Sb is replaced by Sn resulting in changes to the band structure and properties. The structures are investigated by powder diffraction and samples consolidated into fully dense pellets for thermoelectric measurements. The band structure of a reasonable structure, Ca14MgSb7Sn4, is calculated in order to better understand the properties. These Sn containing phases show improved thermoelectric properties over Ca14MgSb11 by increasing the Seebeck while decreasing resistivity without significant impact to the already low thermal conductivity. In addition, a composite phase of Yb14MgSb11 was investigated. Composite phases have been shown to improve both the thermoelectric efficiency and mechanical properties of materials. Here we demonstrate an improved thermoelectric figure of merit, power factor, and mechanical properties for the high-temperature p-type Zintl phase Yb14MgSb11. Composites with 0, 1, 2, 3, 4, 6, 8 volume % 6 – 10 µm reduced Fe powder were prepared via a fast, scalable mechanical milling and spark plasma sintering procedure. Powder X-ray diffraction, scanning electron microscopy, and transmission electron microscopy show that Fe is not incorporated into the Yb14MgSb11 structure. First order reversal curves and scanning electron microscopy images show that the Fe inclusions are larger and closer together with increasing Fe content. Thermogravimetric and differential scanning calorimetry show that the composites are stable up to 1273 K. The elastic constants of the 8 volume % Fe composite were measured by resonant ultrasound spectroscopy and show that Yb14MgSb11 becomes stiffer with increasing Fe volume % and SEM after indentations show crack arresting occurs at the Fe interface. Thermoelectric properties on dense pellets are measured from 300 K – 1273 K. The thermoelectric power factor (PF= $$\frac{S^2}{ρ}$$) increases with increasing Fe content, with the 8 volume % Fe resulting in 40% higher PF than pristine Yb14MgSb11. The increase in PF is attributed to a systematic reduction in electrical resistivity. Peak thermoelectric figure of merit (zT= ($$\frac{S^2T}{κρ}$$) is observed at 3 volume % Fe, an 11% improvement in zT compared to Yb14MgSb11. Yb14MgSb11 composites with Fe are compatible with Ce0.9Fe3.5Co0.5Sb12 for thermoelectric generator couple segmentation.
- Research Organization:
- Univ. of California (United States)
- Sponsoring Organization:
- USDOE Office of Nuclear Energy (NE), Office of Space and Defense Power Systems (NE-75)
- DOE Contract Number:
- NE0008543
- OSTI ID:
- 1580654
- Report Number(s):
- Final Technical Report; 16-10083
- Country of Publication:
- United States
- Language:
- English
Seebeck and Figure of Merit Enhancement by Rare Earth Doping in Yb14-xRExZnSb11 (x = 0.5)
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journal | March 2019 |
Hydride assisted synthesis of the high temperature thermoelectric phase: Yb 14 MgSb 11
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journal | October 2019 |
Improved Power Factor and Mechanical Properties of Composites of Yb14MgSb11 with Iron
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journal | January 2020 |
Optimization of Ca14MgSb11 through Chemical Substitutions on Sb Sites: Optimizing Seebeck Coefficient and Resistivity Simultaneously
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journal | May 2018 |
The remarkable crystal chemistry of the Ca14AlSb11 structure type, magnetic and thermoelectric properties
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journal | March 2019 |
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