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Updated: Jun 13, 2026
08:55
Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses
Published on: June 7, 2018
Ammonia absorption in calcium graphite intercalation compound: in situ neutron diffraction, Raman spectroscopy and
G Srinivas1, A Lovell, N T Skipper
1London Centre For Nanotechnology, University College London, 17-19 Gordon Street, London, WC1H 0AH, United Kingdom. g.srinivas@ucl.ac.uk
Physical Chemistry Chemical Physics : PCCP
|May 1, 2010
Summary
Ammonia absorption irreversibly alters calcium-graphite intercalation compounds (Ca-GIC), causing structural changes and reducing superconductivity. Degassing leads to calcium amide and hydrogen formation.
Area of Science:
- Materials Science
- Solid State Chemistry
- Superconductivity
Background:
- Calcium-graphite intercalation compounds (Ca-GIC) exhibit interesting superconducting properties.
- Understanding structural transformations is key to tuning material properties.
Purpose of the Study:
- To investigate the structural and superconducting changes in Ca-GIC upon ammonia absorption.
- To elucidate the mechanism of ammonia interaction with Ca-GIC.
Main Methods:
- In situ time-of-flight neutron diffraction
- Raman spectroscopy
- Magnetization studies
- Controlled ammonia vapor exposure
Main Results:
- Ammonia absorption induces irreversible structural transformations, forming secondary ammoniated Ca-GIC phases.
- Superconducting CaC(6) phase fraction decreases, and stacking disorder increases.
- Degassing ammoniated Ca-GIC at high temperatures yields calcium amide and hydrogen.
Conclusions:
- Ammonia absorption significantly disrupts the structure and superconductivity of Ca-GIC.
- A molecular stacking model is proposed to explain the observed ammonia absorption and phase transitions.
- The findings offer insights into the chemical stability and degradation pathways of GICs.
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