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Results for “synthesis (scalable processing)”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Electrical characterization and water sensitivity of Sr 2 Fe 1.5 Mo 0.5 O 6-δ as a possible solid oxide fuel cell electrode

Sr 2 Fe 1.5 Mo 0.5 O 6-δ (SFMO) powders were synthesized by combustion synthesis. Porous samples were formed by uniaxial pressing of powder compacts and sintering in air. Electrical conductivity was measured by a four-point DC technique over a temperature range from 200 °C to 800 °C in air and in hydrogen. Crystal structures were investigated by X-ray diffractometry. Stability of powder samples was investigated in H 2 O-containing atmospheres. It was observed that Sr 2 Fe 1.5 Mo 0.5 O 6-δ was stable at 800 °C in water-containing atmospheres. However, it reacts with water at low temperatures. Reaction of Sr 2 Fe 1.5 Mo 0.5 O 6-δ (SFMO) with water at low temperatures is a potential shortcoming of this material for application in solid oxide fuel cells (SOFC) due to concerns regarding degradation of the electrodes at low temperatures during cycling.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

A new n-type half-Heusler thermoelectric material NbCoSb

Highlights: • Half-Heusler alloy NbCoSb with 19 valence electron count was studied as TE material. • It is surprising that NbCoSb is n-type. • A maximum ZT of ∼0.4 is achieved at 700 °C without optimization. • It opens up a new route to develop new half-Heusler thermoelectric materials. • It is very interesting that a traditionally thought of VEC of 18 is not required. - Abstract: We surprisingly made a new n-type thermoelectric compound NbCoSb with half-Heusler (HH) structure having valence electron count of 19, different from the traditional 18, which opens up a new route to develop new half-Heusler thermoelectric materials not following the traditional valence electron count of 18. The samples are made by arc melting followed by ball milling and hot pressing. The effect of hot pressing temperature on the thermoelectric properties of NbCoSb samples has been studied. A maximum thermoelectric figure-of-merit (ZT) of ∼0.4 is achieved at 700 °C in NbCoSb sample that is hot pressed at 1000 °C. This work add a new member to HH compounds for thermoelectric applications, although the peak ZT of ∼0.4 is still lower than that of the traditional HHs. Moreover, it is very interesting to see that a traditionally thought of valence electron counts of 18 is not required.

36 MATERIALS SCIENCE↗
DOE OSTI2017

High thermoelectric performance in (Bi 0.25 Sb 0.75 ) 2 Te 3 due to band convergence and improved by carrier concentration control

Bi 2 Te 3 has been recognized as an important cooling material for thermoelectric applications. Yet its thermoelectric performance could still be improved. Here we propose a band engineering strategy by optimizing the converging valence bands of Bi 2 Te 3 and Sb 2 Te 3 in the (Bi 1-x Sb x ) 2 Te 3 system when x = 0.75. Band convergence successfully explains the sharp increase in density-of-states effective mass yet relatively constant mobility and optical band gap measurement. This band convergence picture guides the carrier concentration tuning for optimum thermoelectric performance. To synthesize homogeneous textured and optimally doped (Bi 0.25 Sb 0.75 ) 2 Te 3 , excess Te was chosen as the dopant. Uniform control of the optimized thermoelectric composition was achieved by zone-melting which utilizes separate solidus and liquidus compositions to obtain zT = 1.05 (at 300 K) without nanostructuring.

36 MATERIALS SCIENCE↗