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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Ba2CaWO6 by Materials Project

Ba2CaWO6 is (Cubic) Perovskite-derived structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Ba2+ is bonded to twelve equivalent O2- atoms to form BaO12 cuboctahedra that share corners with twelve equivalent BaO12 cuboctahedra, faces with six equivalent BaO12 cuboctahedra, faces with four equivalent CaO6 octahedra, and faces with four equivalent WO6 octahedra. All Ba–O bond lengths are 3.02 Å. Ca2+ is bonded to six equivalent O2- atoms to form CaO6 octahedra that share corners with six equivalent WO6 octahedra and faces with eight equivalent BaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All Ca–O bond lengths are 2.30 Å. W6+ is bonded to six equivalent O2- atoms to form WO6 octahedra that share corners with six equivalent CaO6 octahedra and faces with eight equivalent BaO12 cuboctahedra. The corner-sharing octahedral tilt angles are 0°. All W–O bond lengths are 1.96 Å. O2- is bonded in a distorted linear geometry to four equivalent Ba2+, one Ca2+, and one W6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ba2CaWO6 by Materials Project

Ba2CaWO6 crystallizes in the tetragonal I4/m space group. The structure is three-dimensional. Ba2+ is bonded to twelve O2- atoms to form distorted BaO12 cuboctahedra that share corners with twelve equivalent BaO12 cuboctahedra, faces with six equivalent BaO12 cuboctahedra, faces with four equivalent CaO6 octahedra, and faces with four equivalent WO6 octahedra. There are a spread of Ba–O bond distances ranging from 2.84–3.21 Å. Ca2+ is bonded to six O2- atoms to form CaO6 octahedra that share corners with six equivalent WO6 octahedra and faces with eight equivalent BaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–14°. All Ca–O bond lengths are 2.32 Å. W6+ is bonded to six O2- atoms to form WO6 octahedra that share corners with six equivalent CaO6 octahedra and faces with eight equivalent BaO12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–14°. All W–O bond lengths are 1.96 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 2-coordinate geometry to four equivalent Ba2+, one Ca2+, and one W6+ atom. In the second O2- site, O2- is bonded in a distorted linear geometry to four equivalent Ba2+, one Ca2+, and one W6+ atom.

36 MATERIALS SCIENCE↗
NASA NTRS1992

Extended testing of xenon ion thruster hollow cathodes

A hollow cathode wear-test of 508 hours was successfully completed at an emission current of 23.0 A and a xenon flow rate of 10 Pa-L/s. This test was the continuation of a hollow cathode contamination investigation. Discharge voltage was stable at 16.7 V. The cathode temperature averaged 1050 C with a 7 percent drop during the wear-test. Discharge ignition voltage was found to be approximately 20 V and was repeatable over four starts. Post-test analyses of the hollow cathode found a much improved internal cathode condition with respect to earlier wear-test cathodes. Negligible tungsten movement occurred and no formation of mono-barium tungstate was observed. These results correlated with an order-of-magnitude reduction in propellant feed-system leakage rate. Ba2CaWO6 and extensive calcium crystal formation occurred on the upstream end of the insert. Ba-Ca compound depositions were found on the Mo insert collar, on the Re electrical leads, and in the gap between the insert and cathode wall. This wear-test cathode was found to be in the best internal condition and had the most stable operating performance of any hollow cathode tested during this contamination investigation.

Sarver-Verhey, Timothy R.↗
NASA NTRS1992

Extended-testing of xenon ion thruster hollow cathodes

A hollow cathode wear-test of 508 hours was successfully completed at an emission current of 23.0 A and a xenon flow rate of 10 Pa-L/s. This test was the continuation of a hollow cathode contamination investigation. Discharge voltage was stable at 16.7 V. The cathode temperature averaged 1050 C with a 7 percent drop during the wear-test. Discharge ignition voltage was found to be approximately 20 V and was repeatable over four starts. Post-test analyses of the hollow cathode found a much improved internal cathode condition with respect to earlier wear-test cathodes. Negligible tungsten movement occurred and no formation of mono-barium tungsten was observed. These results correlated with an order-of-magnitude reduction in propellant feed-system leakage rate. Ba2CaWO6 and extensive calcium crystal formation occurred on the upstream end of the insert. Ba-Ca compound depositions were found on the Mo insert collar, on the Re electrical leads, and in the gap between the insert and cathode wall. This wear-test cathode was found to be in the best internal condition and had the most stable operating performance of any hollow cathode tested during this contamination investigation.

Sarver-Verhey, Timothy R.↗