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5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on K2NiF4 by Materials Project

K2NiF4 is (La,Ba)CuO4 structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. K1+ is bonded in a 9-coordinate geometry to nine F1- atoms. There are a spread of K–F bond distances ranging from 2.65–2.88 Å. Ni2+ is bonded to six F1- atoms to form corner-sharing NiF6 octahedra. The corner-sharing octahedral tilt angles are 0°. There are two shorter (2.03 Å) and four longer (2.04 Å) Ni–F bond lengths. There are two inequivalent F1- sites. In the first F1- site, F1- is bonded to five equivalent K1+ and one Ni2+ atom to form distorted FK5Ni octahedra that share corners with seventeen FK5Ni octahedra, edges with eight equivalent FK5Ni octahedra, and faces with four equivalent FK4Ni2 octahedra. The corner-sharing octahedra tilt angles range from 0–57°. In the second F1- site, F1- is bonded to four equivalent K1+ and two equivalent Ni2+ atoms to form distorted FK4Ni2 octahedra that share corners with fourteen FK5Ni octahedra, edges with two equivalent FK4Ni2 octahedra, and faces with eight FK5Ni octahedra. The corner-sharing octahedra tilt angles range from 0–57°.

36 MATERIALS SCIENCE↗
NASA NTRS1984

Energy Conversion and Utilization Technologies Program (ECUT) electrocatalysis research

The general field of electrocatalysis, from both the technical and business standpoints is accessed and research areas and approaches most likely to lead to substantial energy/cost savings are identified. The overall approach was to compile and evaluate available information, relying heavily on inputs/recommendations of research managers and technical personnel in responsible positions in industry and at universities. Some promising approaches identified to date include the use of transition metal compounds as electrocatalysts and the use of the new electrochemical photocapacitance spectroscopy (EPS) technique for electrocatalyst characterization/development. For the first time, an oxygen electrocatalyst based on the K2NiF4 structure was synthesized, investigated and compared with a perovskite analog. Results show that this class of materials, based on Ni(3+), forms very efficient and stable O2 anodes in basic solution and suggest that other structure-types be examined in this regard. The very difficult problem of dinitrogen and carbon dioxide electroreductions is addressed through the use of biological model systems which can mimic the enzyme processes in nature.

Warren, L. F.↗
NASA NTRS1987

High-pressure study of the new Y-Ba-Cu-O superconducting compound system

Hydrostatic effects on the superconducting transition temperature of the Y-Ba-Cu-O compound system, resistively, up to 19 kbar are investigated. It is found that pressure has little effect on the superconducting state of Y-Ba-Cu-O, in marked contrast to the behavior of the K2NiF4-phase La-Ba-Cu-O and La-Sr-Cu-O systems. It is suggested that this effect may be due to chemical pressure associated with the smaller Y atoms already present in Y-Ba-Cu-O. X-ray powder-diffraction studies show that the high-temperature superconductivity in Y-Ba-Cu-O can only be attributed to one or more phases with structures different from the cubic perovskite or tetragonal layered ones.

Hor, P. H.↗
NASA NTRS1987

Study of some superconducting and magnetic materials on high T sub c oxide superconductors

On the basis of existing data it appears that the high-temperature superconductivity above 77 K reported here, occurs only in compound systems consisting of a phase other than the K2NiF4 phase. A narrow superconducting transition was obtained with T sub c0 = 98 K and T sub c1 = 94 K in Y-Ba-Cu-O (YBCO). Preliminary results indicate that YBCO is rather different from the layered LaBCO, LaSCO, and LaCCO. While electron-photon interaction cannot be absent from this compound system, nonconventional enhanced superconducting interactions due to interfaces, Resonating Valence Bond (RVB) states, or even a superconducting state beyond the BCS framework, may be required to account for the high T sub c in YBCO. It is believed that study of the possible subtle correlation between magnetism and superconductivity will definitely provide important insight into the superconducting mechanism in YBCO and other oxides.

Wu, M. K.↗
NASA NTRS1987

High-resolution synchrotron X-ray study of the structure of La(1.8)Ba(0.2)CuO(4-y)

X-ray diffraction of La(1.8)Ba(0.2)CuO(4-y) reveals two macroscopically segregated tetragonal (K2NiF4-type) phases of nearly identical lattice parameter. Many peaks show additional broadening upon cooling. This broadening is consistent with a spontaneous monoclinic distortion, with an onset temperature of about 150 K, and is possibly relevant to the superconducting properties. Small single crystals of about 70 micron diameter within the powder aggregate are also studied and show a similar two-phase constituency and a resolvable peak splitting at low temperature.

Moss, S. C.↗