In Situ X-Ray Investigations of Staging and Sequencing In Potassium-Graphite Intercalation Compounds
Misenheimer, Mark Eugene
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https://hdl.handle.net/2142/77381
Description
Title
In Situ X-Ray Investigations of Staging and Sequencing In Potassium-Graphite Intercalation Compounds
Author(s)
Misenheimer, Mark Eugene
Issue Date
1985
Department of Study
Physics
Discipline
Physics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Condensed Matter
Language
eng
Abstract
Experimental investigations, using x-ray diffraction techniques, have been made into the phenomenon of staging in graphite intercalation compounds. These studies have been performed in situ by means of a two-zone, high-temperature, x-ray furnace. The transition from stage 1 to stage 2 is found to be a two-phase process which does not require intermediate steps. For stage n, n (GREATERTHEQ) 2, stage mixing is shown to occur in thermodynamic equilibrium. The amount and relative concentration of admixed stages is seen to be a continuous function of the thermodynamic parameters. However, the transition between stage n and stage n+1 still exhibits a discontinuity which can be characterized as a gap in the allowed concentrations for stage admixing. The size of this gap decreases with increasing stage, i.e., the transition becomes more continuous.
Various proposed theories for staging are discussed. It is concluded that the intercalate-intercalate screened coulomb interaction is the stabilizing force for staging. Stage mixing is seen to be a direct consequence of finite domain size and entropy. It is unclear whether the discontinuous nature of the stage transitions is a true miscibility gap resulting from a first-order transition or whether it is an apparent miscibility gap resulting from the particular form of a predicted second-order transition for staging transitions.
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