Structural phase transitions in alkali graphite intercalation compounds

Thesis/Dissertation · Tue Jan 01 00:00:00 EST 1985

OSTI ID:5499090

Winokur, M J

The structural properties of stage 2 and stage 3 alkali GlC's, prepared from single-crystal graphite, were extensively studied using x-ray scattering techniques. A unified picture for the ordering transitions and low-temperature in-plane structures is presented. The ordering transition is found to be similar in all cases. Alkali in-plane ordering always precedes the c-axis ordering and subsequent formation of an (hcp) structure. All low-temperature ordered in-plane structures belong to a discrete set of long-range commensurate domain structures. A unique in-plane polymorphic transition (T/sub c/ = 95K) in stage 2 potassium can be understood in terms of this model. Two new structural transitions are investigated. The first transition is a continuous inhibition of c-axis order at temperatures below 150K. This disordering transition was observed in stage 2 and stage 3 cesium and stage 2 rubidium samples. The second transition is an unusual polymorphic transformation from an hcp structure to an fcc structure (T/sub c/ approx. 160K) in stage 2 cesium. The question of alkali registry is resolved. At low temperatures, the variations in peak intensity result from ordered domains and displacements of alkali atoms away from carbon centers at the walls. At high temperatures, above the ordering transition, stage n greater than or equal to 2 alkali GlC's are found to be intermediate between a lattice liquid and a 2-D fluid.

• Research Organization: Michigan Univ., Ann Arbor (USA)
• OSTI ID: 5499090
• Resource Relation: Other Information: Thesis (Ph. D.)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALKALI METAL COMPOUNDS
PHASE TRANSFORMATIONS
CLATHRATES
GRAPHITE
CRITICAL TEMPERATURE
CRYSTAL LATTICES
ORDER PARAMETERS
CARBON
CRYSTAL STRUCTURE
ELEMENTAL MINERALS
ELEMENTS
MINERALS
NONMETALS
PHYSICAL PROPERTIES
THERMODYNAMIC PROPERTIES
TRANSITION TEMPERATURE
360602* - Other Materials- Structure & Phase Studies