Structural transitions in alkali-graphite intercalation compounds

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1988

OSTI ID:5211521

Cajipe, V B

Structural transitions induced by pressure, temperature, and chemical potential changes were studied in alkali-graphite intercalation compounds using x-ray diffraction. A unique first-order commensurate-commensurate transition was observed at high pressure in KC{sub s}; this in-plane densification is consistent with observation of a fractional stage which occurs during the accompanying sequence of staging transitions. At low temperatures, stage 2 and stages 4 to 10 potassium graphite compounds were found to undergo both in-plane and stage ordering transitions. The room temperature in-plane fluid structure expanded upon freezing to a commensurate solid in stages n {ge} 5 and to a weakly incommensurate superlattice in stage 4 + 5; no out-of-plane correlations were found in these cases suggesting an upper limit of n = 4 for the appearance of 3D effects. The nature of the freezing transition changed with stage according to the symmetry of the low-temperature phase. Using the Hendricks-Teller model for one-dimensional disorder, the average stage and stage disorder in these compounds were shown to decrease with low temperature. Overall, the stage disorder in these metastable constant concentration samples was shown to decrease with stage as predicted by the domain model. This effect was found to persist under equilibrium conditions for cesium graphite.

• Research Organization: Pennsylvania Univ., Philadelphia, PA (USA)
• OSTI ID: 5211521
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360602* -- Other Materials-- Structure & Phase Studies
ALKALI METAL COMPOUNDS
CARBON
CESIUM COMPOUNDS
CLATHRATES
COHERENT SCATTERING
DIFFRACTION
ELEMENTAL MINERALS
ELEMENTS
GRAPHITE
MINERALS
NONMETALS
PHASE TRANSFORMATIONS
POTASSIUM COMPOUNDS
SCATTERING
TEMPERATURE EFFECTS
X-RAY DIFFRACTION