Clathrates of Tetrel elements (Si, Ge, Sn) have attracted interest for their potential use in batteries and other applications. Sodium-filled silicon clathrates are conventionally synthesized through thermal decomposition of the Zintl precursor Na4Si4, but phase selectivity of the product is often difficult to achieve. Herein, we report the selective formation of the type I clathrate Na8Si46using electrochemical oxidation at 450 °C and 550 °C. A two-electrode cell design inspired by high-temperature sodium-sulfur batteries is employed, using Na4Si4as working electrode, Na
Computational methods are increasingly being incorporated into the exploitation of microstructure–property relationships for microstructure-sensitive design of materials. In the present work, we propose non-intrusive materials informatics methods for the high-throughput exploration and analysis of a synthetic microstructure space using a machine learning-reinforced multi-phase-field modeling scheme. We specifically study the interface energy space as one of the most uncertain inputs in phase-field modeling and its impact on the shape and contact angle of a growing phase during heterogeneous solidification of secondary phase between solid and liquid phases. We evaluate and discuss methods for the study of sensitivity and propagation of uncertainty in these input parameters as reflected on the shape of the Cu6Sn5intermetallic during growth over the Cu substrate inside the liquid Sn solder due to uncertain interface energies. The sensitivity results rank
- Award ID(s):
- 2001333
- NSF-PAR ID:
- 10361289
- Publisher / Repository:
- Springer Science + Business Media
- Date Published:
- Journal Name:
- Materials Theory
- Volume:
- 6
- Issue:
- 1
- ISSN:
- 2509-8012
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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β″ -alumina solid electrolyte, and counter electrode consisting of molten Na or Sn. Galvanostatic intermittent titration is implemented to observe the oxidation characteristics and reveals a relatively constant cell potential under quasi-equilibrium conditions, indicating a two-phase reaction between Na4Si4and Na8Si46. We further demonstrate that the product selection and morphology can be altered by tuning the reaction temperature and Na vapor pressure. Room temperature lithiation of the synthesized Na8Si46is evaluated for the first time, showing similar electrochemical characteristics to those in the type II clathrate Na24Si136. The results show that solid-state electrochemical oxidation of Zintl phases at high temperatures can lead to opportunities for more controlled crystal growth and a deeper understanding of the formation processes of intermetallic clathrates. -
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Solid solutions of Mg 2 Si and Mg 2 Sn are promising thermoelectric materials owing to their high thermoelectric figures-of-merit and non-toxicity, but they may undergo phase separation under thermal cycling due to the presence of miscibility gaps, implying that the thermoelectric properties could be significantly degraded during thermoelectric device operation. Herein, this study investigates the strain-induced suppression of the miscibility gap in solid solutions of Mg 2 Si and Mg 2 Sn. Separately prepared Mg 2 Si and Mg 2 Sn powders were made into (Mg 2 Si) 0.7 (Mg 2 Sn) 0.3 mixtures using a high energy ball-milling method followed by spark plasma sintering. Afterwards, the phase evolution of the mixtures, depending on thermal annealing and mixing conditions, was studied experimentally and theoretically. Transmission electron microscopy and X-ray diffraction results show that, despite the presence of a miscibility gap in the pseudo-binary phase diagram, the initial mixture of Mg 2 Si and Mg 2 Sn evolved towards a solid solution state after annealing for 3 hours at 720 °C. Thermodynamic analysis as well as phase-field microstructure simulations show that the strain energy due to the coherent spinodal effect suppresses the chemical spinodal entirely and prevents phase separation. This strategy to suppress the miscibility gap induced by lattice strain through non-equilibrium processing can benefit the thermoelectric figure-of-merit by maximizing phonon alloy scattering. Furthermore, stable solid solutions by engineering phase diagrams have the potential to facilitate the reliable long term operation of thermoelectric generators under continuous thermal loads.more » « less
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Summary We combined optical and atomic force microscopy to observe morphology and kinetics of microstructures (typically referred to as bees) that formed at free surfaces of unmodified Performance Graded (PG) 64‐22 asphalt binders upon cooling from 150°C to room temperature (RT) at 5°C min–1, and changes in these microstructures when the surface was terminated with a transparent solid (glass) or liquid (glycerol) overlayer. The main findings are: (1) at free binder surfaces, wrinkled microstructures started to form near the crystallization temperature (∼45°C) of saturates such as wax observed by differential scanning calorimetry, then grew to ∼5 µm diameter, ∼25 nm wrinkle amplitude and 10–30% surface area coverage upon cooling to RT, where they persisted indefinitely without observable change in shape or density. (2) Glycerol coverage of the binder surface during cooling reduced wrinkled area and wrinkle amplitude three‐fold compared to free binder surfaces upon initial cooling to RT; continued glycerol coverage at RT eliminated most surface microstructures within ∼4 h. (3) No surface microstructures were observed to form at binder surfaces covered with glass. (4) Submicron bulk microstructures were observed by near‐infrared microscopy beneath the surfaces of all binder samples, with size, shape and density independent of surface coverage. No tendency of such structures to float to the top or sink to the bottom of mm‐thick samples was observed. (5) We attribute the dependence of surface wrinkling on surface coverage to variation in interface tension, based on a thin‐film continuum mechanics model.
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