Abstract Thermoelectric materials offer a unique solution for active cooling or conversion of heat to electricity within a thermal protection system due to their solid-state nature. Yet, the integration of thermoelectrics into thermal protection systems is hindered by conventional manufacturing processes, which limit the material’s shape. Laser additive manufacturing can enable freeform shapes that allow integration of thermoelectrics into systems that are favorable for thermoelectric energy conversion. Through modeling and experimentation, this work presents single melt line processing and structures of silicon germanium, a high-temperature thermoelectric material, for laser powder bed fusion. Experiments consisted of single melt lines with an Nd-YAG laser and 50-µm spot size on Si50Ge50and Si80Ge20powder compacts. We found that laser processing of silicon germanium alloys causes oxidation and processing defects that are resolved through rescanning strategies. Rapid cooling results in a microstructure with silicon-rich grains and germanium entrapped near grain boundaries for Si80Ge20and dendritic structures in Si50Ge50which are linked to the degree of undercooling during solidification. Laser-processed silicon germanium contains crystalline defects, nanoscale precipitates, and an average grain size of 24 µm. This work informs laser additive manufacturing of silicon germanium parts and uncovers process-structure relationships of laser-processed silicon germanium alloys.
more »
« less
Zintl Phases as Reactive Precursors for Synthesis of Novel Silicon and Germanium-Based Materials
Recent experimental and theoretical work has demonstrated significant potential to tune the properties of silicon and germanium by adjusting the mesostructure, nanostructure, and/or crystalline structure of these group 14 elements. Despite the promise to achieve enhanced functionality with these already technologically important elements, a significant challenge lies in the identification of effective synthetic approaches that can access metastable silicon and germanium-based extended solids with a particular crystal structure or specific nano/meso-structured features. In this context, the class of intermetallic compounds known as Zintl phases has provided a platform for discovery of novel silicon and germanium-based materials. This review highlights some of the ways in which silicon and germanium-based Zintl phases have been utilized as precursors in innovative approaches to synthesize new crystalline modifications, nanoparticles, nanosheets, and mesostructured and nanoporous extended solids with properties that can be very different from the ground states of the elements.
more »
« less
- PAR ID:
- 10097281
- Date Published:
- Journal Name:
- Materials
- Volume:
- 12
- Issue:
- 7
- ISSN:
- 1996-1944
- Page Range / eLocation ID:
- 1139
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Clathrates have been reported to form in a variety of different structure types; however, inorganic clathrate-I materials with a low-cation concentration have yet to be investigated. Furthermore, tin-based compositions have been much less investigated as compared to silicon or germanium analogs. We report the temperature-dependent structural and thermal properties of single-crystal Eu 2 Ga 11 Sn 35 revealing the effect of structure and composition on the thermal properties of this low-cation clathrate-I material. Specifically, low-temperature heat capacity, thermal conductivity, and synchrotron single-crystal x-ray diffraction reveal a departure from Debye-like behavior, a glass-like phonon mean-free path for this crystalline material, and a relatively large Grüneisen parameter due to the dominance of low-frequency Einstein modes. Our analyses indicate thermal properties that are a direct result of the structure and composition of this clathrate-I material.more » « less
-
Abstract MAX phases are layered solids with unique properties combining characteristics of ceramics and metals. MXenes are their two‐dimensional siblings that can be synthesized as van der Waals‐stacked and multi‐/single‐layer nanosheets, which possess chemical and physical properties that make them interesting for a plethora of applications. Both families of materials are highly versatile in terms of their chemical composition and theoretical studies suggest that many more members are stable and can be synthesized. This is very intriguing because new combinations of elements, and potentially new structures, can lead to further (tunable) properties. In this review, we focus on the synthesis science (including non‐conventional approaches) and structure of members less investigated, namely compounds with more exoticM‐,A‐, andX‐elements, for example nitrides and (carbo)nitrides, and the related family of MAB phases.more » « less
-
The calcium- and strontium- alumo-germanides SrxCa1–xAl2Ge2 (x ≈ 0.4) and SrAl2Ge2 have been synthesized and structurally characterized. Additionally, a binary calcium germanide CaGe has also been identified as a byproduct. All three crystal structures have been established from single-crystal X-ray diffraction methods and refined with high accuracy and precision. The binary CaGe crystallizes with a CrB-type structure in the orthorhombic space group Cmcm (no. 63; Z = 4; Pearson symbol oC8), where the germanium atoms are interconnected into infinite zigzag chains, formally [Ge]2−. The calcium atoms are arranged in monocapped trigonal prisms, centered by Ge atoms. SrxCa1−xAl2Ge2 (x ≈ 0.4) and SrAl2Ge2 have been confirmed to crystallize with a CaAl2Si2-type structure in the trigonal space group P3¯m1 (no. 164; Z = 1; Pearson symbol hP5), where the germanium and aluminum atoms form puckered double-layers, formally [Al2Ge2]2−. The calcium atoms are located between the layers and reside inside distorted octahedra of Ge atoms. All presented structures have a valence electron count satisfying the octet rules (e.g., Ca2+Ge2− and Ca2+[Al2Ge2]2−) and can be regarded as Zintl phases.more » « less
-
Computational prediction of good thermoelectric (TE) performance in several n-type doped Zintl phases, combined with successful experimental realization, has sparked interest in discovering new n-type dopable members of this family of materials. However, most known Zintls are typically only p-type dopable; prior successes in finding n-type Zintl phases have been largely serendipitous. Here, we go beyond previously synthesized Zintl phases and perform chemical substitutions in known n-type dopable ABX Zintl phases to discover new ones. We use first-principles calculations to predict their stability, potential for TE performance as well as their n-type dopability. Using this approach, we find 17 new ABX Zintl phases in the KSnSb structure type that are predicted to be stable. Several of these newly predicted phases (KSnBi, RbSnBi, NaGeP) are found to exhibit promising n-type TE performance and are n-type dopable. We propose these compounds for further experimental studies, especially KSnBi and RbSnBi, which are both predicted to be good TE materials with high electron concentrations due to self-doping by native defects, when grown under alkali-rich conditions.more » « less
An official website of the United States government

