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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Thermal transport in Yb-based 1-2-20 materials

Abstract Lattice thermal-transport properties of heavy-fermion YbT 2 Zn 20 -based (T = Co, Rh, and Ir) 1-2-20 compounds are calculated with the single-mode relaxation-time approximation and the full solution of the linearized phonon Boltzmann transport equation from first-principles anharmonic phonon calculations. We predict low lattice thermal conductivity κ L with a maximum value of ∼ 24.16 · K at 85.14 K, 137.29 · K at 9.67 K, and 23.55 · K at 67.50 K and ∼ 12.02, 40.04, and 10.30 · K at room temperature for YbCo 2 Zn 20 , YbRh 2 Zn 20 , and YbIr 2 Zn 20 , respectively. Based on the analysis of the cumulative κ L as a function of the phonon mean free path and the frequency-dependent joint density of states at various temperatures, we attribute the low κ L to a rattling mode with an average characteristic rattling frequency that enhanced phonon scattering processes, which reduced the phonon mean free paths, suppressed the phonon lifetime, and enhanced the probability of three-phonon scattering events. The predicted low κ L , especially in YbCo 2 Zn 20 and YbIr 2 Zn 20 , makes them promising candidate materials for thermoelectric applications and thermal management.

Physics↗
NASA NTRS1995

Efficient Quenching of Population Trapping in Excited Yb(+)

We report on a study to determine the efficiency of various buffer gases in quenching the population trapping states of laser-excited ytterbium ions. The ions were confined in an rf-dc hybrid trap, and their (2)S(.5) left and right arrow (2)P(3/2) transition was excited with 329-nm laser light. Buffer gases used include H2, N2, CO2, Ar, and He at several different pressure regimes. We have identified N2 to be highly efficient in quenching the population of the trapping states and thus be the most suitable buffer gas to use with ytterbium for the development of a trapped-ion microwave frequency standard.

Seidel, D. J.↗
NASA NTRS1994

Efficient Quenching of Population Trapping in Excited Yb superscript +

The efficiency of various buffer gases in quenching the population trapping states of laser excited ytterbium ions is described. Highly efficient in quenching the population of the trapping states, N subscript 2 has been identified as the most suitable buffer gas to use with ytterbium for the development i=of a trapped ion microwave frequency standard.

Buffer gases↗
NASA NTRSDate not supplied

Foreign Object Damage in Yb 2 Si 2 O 7 Environmental Barrier Coatings

Environmental Barrier Coatings (EBCs) have been developed as an enabling technology for silicon carbide based ceramic matrix composites in gas turbine engines. Two of the key failure mechanisms identified in EBC systems are foreign object damage (FOD) and the oxidative growth of a SiO 2 thermally grown oxide (TGO) layer that can lead to premature coating spallation. Previously the effects of FOD on NASA’s second generation Ytterbium Disilicate EBC were studied and recently it was shown that the addition of oxide modifiers resulted in improved oxidation resistance in the EBC. This work will compare FOD of the baseline Ytterbium Disilicate EBC to the that of the modified EBC. FOD was performed at room temperature using a 1.59 mm hardened steel ball with projectile velocities of 50-300 m/s. Additionally, the effects of oxidation via cyclic steam exposure prior to impact were investigated.

environmental barrier coatings (EBCs)↗