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Title: Characterization of the structure of LaD{sub 2.50} by neutron powder diffraction

Abstract

Neutron powder diffraction (NPD) measurments of the rare-earth deuteride LaD{sub 2.50} were undertaken between 10 and 430 K. Rietveld refinements indicated that, above {approximately} 385 K, the LaD{sub 2.50} structure is cubic (Fm3m) with deuterium fully occupying the tetrahedral (t) interstices of the fcc La lattice and the excess deuterium occupying a portion of the octahedral (o) interstices with full statistical disorder. As the temperature is decreased below {approximately} 385 K, the LaD{sub 2.50} structure undergoes a tetragonal distortion concomitant with the onset of deuterium long-range order (I4{sub 1}/amd) in the o sublattice, similar to previous structural results for the light-rare-earth deuterides RD{sub 2+x} for 0.3 < x < 0.5. Fully developed long-range order is established in the vicinity of 200 to 230 K. Considering the o sublattice as residing in a family of (042){sub Cubic} planes, perfect long-range order can be described as a repeating four-plane sequence comprised of two consecutive planes possessing fully occupied o sites followed by two consecutive planes possessing fully vacant o sites. This ordering is accompanied by correlated basal-plane displacements of the t-site deuterium atoms along either the a or b axes in response to repulsive interactions with the nearest-neighbor D{sub o} atoms. Moreover,more » the c-directed La-D{sub o} bond distances are decreased by a displacement of the La atoms toward the D{sub o} atoms.« less

Authors:
; ;  [1]
  1. National Inst. of Standards and Technology, Gaithersburg, MD (United States)
Publication Date:
OSTI Identifier:
263734
Resource Type:
Journal Article
Journal Name:
Journal of Solid State Chemistry
Additional Journal Information:
Journal Volume: 122; Journal Issue: 1; Other Information: PBD: 15 Feb 1996
Country of Publication:
United States
Language:
English
Subject:
40 CHEMISTRY; 36 MATERIALS SCIENCE; LANTHANUM COMPOUNDS; PHASE STUDIES; DEUTERIUM COMPOUNDS; TETRAGONAL LATTICES; NEUTRON DIFFRACTION; CRYSTAL STRUCTURE; VACANCIES

Citation Formats

Udovic, T J, Huang, Q, and Rush, J J. Characterization of the structure of LaD{sub 2.50} by neutron powder diffraction. United States: N. p., 1996. Web. doi:10.1006/jssc.1996.0096.
Udovic, T J, Huang, Q, & Rush, J J. Characterization of the structure of LaD{sub 2.50} by neutron powder diffraction. United States. https://doi.org/10.1006/jssc.1996.0096
Udovic, T J, Huang, Q, and Rush, J J. Thu . "Characterization of the structure of LaD{sub 2.50} by neutron powder diffraction". United States. https://doi.org/10.1006/jssc.1996.0096.
@article{osti_263734,
title = {Characterization of the structure of LaD{sub 2.50} by neutron powder diffraction},
author = {Udovic, T J and Huang, Q and Rush, J J},
abstractNote = {Neutron powder diffraction (NPD) measurments of the rare-earth deuteride LaD{sub 2.50} were undertaken between 10 and 430 K. Rietveld refinements indicated that, above {approximately} 385 K, the LaD{sub 2.50} structure is cubic (Fm3m) with deuterium fully occupying the tetrahedral (t) interstices of the fcc La lattice and the excess deuterium occupying a portion of the octahedral (o) interstices with full statistical disorder. As the temperature is decreased below {approximately} 385 K, the LaD{sub 2.50} structure undergoes a tetragonal distortion concomitant with the onset of deuterium long-range order (I4{sub 1}/amd) in the o sublattice, similar to previous structural results for the light-rare-earth deuterides RD{sub 2+x} for 0.3 < x < 0.5. Fully developed long-range order is established in the vicinity of 200 to 230 K. Considering the o sublattice as residing in a family of (042){sub Cubic} planes, perfect long-range order can be described as a repeating four-plane sequence comprised of two consecutive planes possessing fully occupied o sites followed by two consecutive planes possessing fully vacant o sites. This ordering is accompanied by correlated basal-plane displacements of the t-site deuterium atoms along either the a or b axes in response to repulsive interactions with the nearest-neighbor D{sub o} atoms. Moreover, the c-directed La-D{sub o} bond distances are decreased by a displacement of the La atoms toward the D{sub o} atoms.},
doi = {10.1006/jssc.1996.0096},
url = {https://www.osti.gov/biblio/263734}, journal = {Journal of Solid State Chemistry},
number = 1,
volume = 122,
place = {United States},
year = {1996},
month = {2}
}