Neutron diffraction study of potassium-graphite intercalation compounds at high pressure: Staging transitions and one-dimensional disorder

Journal Article · Wed Jan 15 04:00:00 EST 1986 · Phys. Rev. B: Condens. Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.33.1329· OSTI ID:6345491

Kim, H J; Fischer, J E; McWhan, D B; Axe, J D

Detailed (00L) neutron scattering profiles have been measured versus hydrostatic pressure (0 < P < 20 kbar) at room temperature for potassium-graphite intercalation compounds KC/sub x/ with 8 < x < 40. The average density of filled galleries along the c axis decreases with increasing P, implying a concomitant increase in the (average) areal K density within a gallery. We observe both large P regions exhibiting continuous evolution of different stages, and narrow P regions where the average stage changes abruptly. The Hendricks-Teller model of one-dimensional disorder is used to fit entire diffraction profiles over extended q ranges. Some of the high-P staging and disorder effects are attributable to P-induced in-plane intercalate densification, the sequence of gallery occupancy and its perfection being a secondary consequence. Other features are entirely controlled by interlayer interactions: e.g., a pure stage-4 phase evolves asymptotically with increasing P at 6-7 kbar for 36 < x < 39, whereas a commensurate 2 x 2 in-plane density would be compatible with a pure stage-4 phase only for x=32.0. We demonstrate from the fits that the fractional stage-(3/2) phase in KC8, reported earlier by us to occur between 15 and 19 kbar, exhibits c-axis correlations no worse than other high-P phases, indicating that this unusual structure represents a true equilibrium phase and does not result simply from random layer sequencing.

• Research Organization: Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania 19104
• DOE Contract Number: AC02-76CH00016
• OSTI ID: 6345491
• Journal Information: Phys. Rev. B: Condens. Matter; (United States), Journal Name: Phys. Rev. B: Condens. Matter; (United States) Vol. 33:2; ISSN PRBMD
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360603* -- Materials-- Properties
ALKALI METALS
AUGMENTATION
CARBON
CLATHRATES
COHERENT SCATTERING
DENSITY
DIFFRACTION
ELEMENTAL MINERALS
ELEMENTS
GRAPHITE
HIGH PRESSURE
LAYERS
METALS
MINERALS
NEUTRON DIFFRACTION
NONMETALS
PHYSICAL PROPERTIES
POTASSIUM
PRESSURE DEPENDENCE
SCATTERING
SPECTRA