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Title: Structural studies of Hydrogenation and Dehydrogenation of Li 3N using in situ neutron diffraction

Abstract

In situ neutron diffraction studies were carried out on the hydrogen absorption and desorption of pure alpha Lithium Nitride. When the sample was exposed to deuterium gas (2H2) at 150C we observed no absorption for twelve hours. We observed an incomplete reaction between the Nitride and D2 at 200C with a 4% uptake. At 250C we observed a total of 7.2% hydrogen uptake. Interestingly we also observed a change in the volume of Li Imide during absorption and desorption at 250C indicating a possible stoichiometry change during this process. At the end of the experiment when the sample was cooled down to room temperature we observed two cubic phases in the sample with slightly different lattice parameters. This implies that in situ studies of the material are crucial to understand the reaction mechanism as the quenched sample exhibits rather different behavior than the sample under reaction conditions.

Authors:
 [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
931981
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry C; Journal Volume: 111
Country of Publication:
United States
Language:
English
Subject:
08 HYDROGEN; ABSORPTION; DEHYDROGENATION; DESORPTION; DEUTERIUM; HYDROGEN; HYDROGENATION; IMIDES; LATTICE PARAMETERS; LITHIUM NITRIDES; NEUTRON DIFFRACTION; NITRIDES; REACTION KINETICS; STOICHIOMETRY; Hydrogen Absorbing material; Metal Nitride; Neutron Diffraction

Citation Formats

Huq, Ashfia. Structural studies of Hydrogenation and Dehydrogenation of Li3N using in situ neutron diffraction. United States: N. p., 2007. Web.
Huq, Ashfia. Structural studies of Hydrogenation and Dehydrogenation of Li3N using in situ neutron diffraction. United States.
Huq, Ashfia. Mon . "Structural studies of Hydrogenation and Dehydrogenation of Li3N using in situ neutron diffraction". United States. doi:.
@article{osti_931981,
title = {Structural studies of Hydrogenation and Dehydrogenation of Li3N using in situ neutron diffraction},
author = {Huq, Ashfia},
abstractNote = {In situ neutron diffraction studies were carried out on the hydrogen absorption and desorption of pure alpha Lithium Nitride. When the sample was exposed to deuterium gas (2H2) at 150C we observed no absorption for twelve hours. We observed an incomplete reaction between the Nitride and D2 at 200C with a 4% uptake. At 250C we observed a total of 7.2% hydrogen uptake. Interestingly we also observed a change in the volume of Li Imide during absorption and desorption at 250C indicating a possible stoichiometry change during this process. At the end of the experiment when the sample was cooled down to room temperature we observed two cubic phases in the sample with slightly different lattice parameters. This implies that in situ studies of the material are crucial to understand the reaction mechanism as the quenched sample exhibits rather different behavior than the sample under reaction conditions.},
doi = {},
journal = {Journal of Physical Chemistry C},
number = ,
volume = 111,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • No abstract prepared.
  • Motivated by predictions made using a bond valence sum difference map (BVS-DM) analysis, the novel Li-ion conductor Li 2Mg 2P 3O 9N was synthesized in this paper by ion exchange from a Na 2Mg 2P 3O 9N precursor. Impedance spectroscopy measurements indicate that Li 2Mg 2P 3O 9N has a room temperature Li-ion conductivity of about 10 –6 S/cm (comparable to LiPON), which is 6 orders of magnitude higher than the extrapolated Na-ion conductivity of Na 2Mg 2P 3O 9N at this temperature. The structure of Li 2Mg 2P 3O 9N was determined from ex situ synchrotron and time-of-flight neutronmore » diffraction data to retain the P2 13 space group, though with a cubic lattice parameter of a = 9.11176(8) Å that is significantly smaller than the a = 9.2439(1) Å of Na 2Mg 2P 3O 9N. The two Li-ion sites are found to be very substantially displaced (~0.5 Å) relative to the analogous Na sites in the precursor phase. The non-molten salt ion exchange method used to prepare Li 2Mg 2P 3O 9N produces a minimal background in powder diffraction experiments, and was therefore exploited for the first time to follow a Li +/Na + ion exchange reaction using in situ powder neutron diffraction. Lattice parameter changes during ion exchange suggest that the reaction proceeds through a Na 2–xLi xMg 2P 3O 9N solid solution (stage 1) followed by a two-phase reaction (stage 2) to form Li 2Mg 2P 3O 9N. However, full Rietveld refinements of the in situ neutron diffraction data indicate that the actual transformation mechanism is more complex and instead involves two thermodynamically distinct solid solutions in which the Li exclusively occupies the Li1 site at low Li contents (stage 1a) and then migrates to the Li3 site at higher Li contents (stage 1b), a crossover driven by the different signs of the local volume change at these sites. Finally, in addition to highlighting the importance of obtaining full structural data in situ throughout the ion exchange process, these results provide insights into the general question of what constitutes a thermodynamic phase.« less
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