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Hydrogenation induced structure and property changes in GdGa

Nedumkandathil, Reji; Kranak, Verina F.; Johansson, Robert; Ångström, Jonas; Balmes, Olivier LU ; Andersson, Mikael S.; Nordblad, Per; Scheicher, Ralph H.; Sahlberg, Martin and Häussermann, Ulrich (2016) In Journal of Solid State Chemistry 239. p.184-191
Abstract

Hydrides GdGaHx were obtained by exposing the Zintl phase GdGa with the CrB structure to a hydrogen atmosphere at pressures from 1.5 to 50 bar and temperatures from 50 to 500 °C. Structural analysis by powder X-ray diffraction suggests that conditions with hydrogen pressures in a range between 15 and 50 bar and temperatures below 500 °C afford a uniform hydride phase with the NdGaH1.66 structure (Cmcm, a=3.9867(7) Å, b=12.024(2) Å, c=4.1009(6) Å) which hosts H in two distinct positions, H1 and H2. H1 is coordinated in a tetrahedral fashion by Gd atoms, whereas H2 atoms are inserted between Ga atoms. The assignment of the NdGaH1.66 structure is corroborated by first principles DFT calculations. Modeling... (More)

Hydrides GdGaHx were obtained by exposing the Zintl phase GdGa with the CrB structure to a hydrogen atmosphere at pressures from 1.5 to 50 bar and temperatures from 50 to 500 °C. Structural analysis by powder X-ray diffraction suggests that conditions with hydrogen pressures in a range between 15 and 50 bar and temperatures below 500 °C afford a uniform hydride phase with the NdGaH1.66 structure (Cmcm, a=3.9867(7) Å, b=12.024(2) Å, c=4.1009(6) Å) which hosts H in two distinct positions, H1 and H2. H1 is coordinated in a tetrahedral fashion by Gd atoms, whereas H2 atoms are inserted between Ga atoms. The assignment of the NdGaH1.66 structure is corroborated by first principles DFT calculations. Modeling of phase and structure stability as a function of composition resulted in excellent agreement with experimental lattice parameters when x=1.66 and revealed the presence of five-atom moieties Ga-H2-Ga-H2-Ga in GdGaH1.66. From in situ powder X-ray diffraction using synchrotron radiation it was established that hydrogenation at temperatures above 200 °C affords a hydride with x≈1.3, which is stable up to 500 °C, and that additional H absorption, yielding GdGaH1.66, takes place at lower temperatures. Consequently, GdGaH1.66 desorbs H above T=200 °C. Without the presence of hydrogen, hydrides GdGaHx decompose at temperatures above 300 °C into GdH2 and an unidentified Gd-Ga intermetallics. Thus the hydrogenation of GdGa is not reversible. From magnetic measurements the Curie-Weiss constant and effective magnetic moment of GdGaH1.66 were obtained. The former indicates antiferromagnetic interactions, the latter attains a value of ~8 μB which is typical for compounds containing Gd3+ions.

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organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
in situ powder diffraction, Metal hydrides, Zintl phases
in
Journal of Solid State Chemistry
volume
239
pages
8 pages
publisher
Elsevier
external identifiers
  • Scopus:84966350634
ISSN
0022-4596
DOI
10.1016/j.jssc.2016.04.028
language
English
LU publication?
yes
id
ba40136d-92a8-4baf-8f38-f0263bfd6b59
date added to LUP
2016-09-27 11:29:09
date last changed
2016-09-27 11:29:09
@misc{ba40136d-92a8-4baf-8f38-f0263bfd6b59,
  abstract     = {<p>Hydrides GdGaH<sub>x</sub> were obtained by exposing the Zintl phase GdGa with the CrB structure to a hydrogen atmosphere at pressures from 1.5 to 50 bar and temperatures from 50 to 500 °C. Structural analysis by powder X-ray diffraction suggests that conditions with hydrogen pressures in a range between 15 and 50 bar and temperatures below 500 °C afford a uniform hydride phase with the NdGaH<sub>1.66</sub> structure (Cmcm, a=3.9867(7) Å, b=12.024(2) Å, c=4.1009(6) Å) which hosts H in two distinct positions, H1 and H2. H1 is coordinated in a tetrahedral fashion by Gd atoms, whereas H2 atoms are inserted between Ga atoms. The assignment of the NdGaH<sub>1.66</sub> structure is corroborated by first principles DFT calculations. Modeling of phase and structure stability as a function of composition resulted in excellent agreement with experimental lattice parameters when x=1.66 and revealed the presence of five-atom moieties Ga-H2-Ga-H2-Ga in GdGaH<sub>1.66</sub>. From in situ powder X-ray diffraction using synchrotron radiation it was established that hydrogenation at temperatures above 200 °C affords a hydride with x≈1.3, which is stable up to 500 °C, and that additional H absorption, yielding GdGaH<sub>1.66</sub>, takes place at lower temperatures. Consequently, GdGaH<sub>1.66</sub> desorbs H above T=200 °C. Without the presence of hydrogen, hydrides GdGaH<sub>x</sub> decompose at temperatures above 300 °C into GdH<sub>2</sub> and an unidentified Gd-Ga intermetallics. Thus the hydrogenation of GdGa is not reversible. From magnetic measurements the Curie-Weiss constant and effective magnetic moment of GdGaH<sub>1.66</sub> were obtained. The former indicates antiferromagnetic interactions, the latter attains a value of ~8 μ<sub>B</sub> which is typical for compounds containing Gd<sup>3+</sup>ions.</p>},
  author       = {Nedumkandathil, Reji and Kranak, Verina F. and Johansson, Robert and Ångström, Jonas and Balmes, Olivier and Andersson, Mikael S. and Nordblad, Per and Scheicher, Ralph H. and Sahlberg, Martin and Häussermann, Ulrich},
  issn         = {0022-4596},
  keyword      = {in situ powder diffraction,Metal hydrides,Zintl phases},
  language     = {eng},
  month        = {07},
  pages        = {184--191},
  publisher    = {ARRAY(0x9aeef40)},
  series       = {Journal of Solid State Chemistry},
  title        = {Hydrogenation induced structure and property changes in GdGa},
  url          = {http://dx.doi.org/10.1016/j.jssc.2016.04.028},
  volume       = {239},
  year         = {2016},
}