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Structural Studies of Hydrogen Storage Alloys using X-ray/Neutron Diffraction and Total Scattering

Published online by Cambridge University Press:  22 August 2011

Yumiko Nakamura
Affiliation:
National Institute of Advanced Industrial Science and Technology, AIST Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan
Hyunjeong Kim
Affiliation:
National Institute of Advanced Industrial Science and Technology, AIST Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan
Saishun Yamazaki
Affiliation:
National Institute of Advanced Industrial Science and Technology, AIST Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan
Kouji Sakaki
Affiliation:
National Institute of Advanced Industrial Science and Technology, AIST Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan
Thomas Proffen
Affiliation:
Los Alamos National Laboratory, Los Alamos, NM87545, USA
Etsuo Akiba
Affiliation:
National Institute of Advanced Industrial Science and Technology, AIST Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan
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Abstract

Crystal and local structures and hydrogen occupation of Mg containing materials, (Mg,Ca)Nix (x = 2, 3) intermetallic compounds and a MgCo metastable alloy, have been investigated using in-situ and ex-situ X-ray/neutron diffraction and total scattering.

A C15 Laves phase (Mg0.67Ca0.33)Ni2 showed isotropic lattice expansion upon hydrogenation. Mg and Ca occupied the same site randomly. It has two hydrogen sites, Mg(Ca)2Ni2 site and M(Ca)Ni3 site.

Mg2CaNi9, MgCa2Ni9, and CaNi3 compounds consisted of MgZn2-type (Mg,Ca)2Ni4 cell and CaCu5-type CaNi5 cell stacking along the c-axis. The MgZn2-type cell was occupied by only Mg in Mg2CaNi9, and randomly occupied by both Mg and Ca in MgCa2Ni9. Expansion of this cell strongly depended on the composition: larger expansion was observed in a Ca-rich composition.

Local structure of a Mg-Co alloy synthesized by mechanical alloying has been studied using the PDF (Pair Distribution Function) method. The analysis suggested that material contained two 1-2 nm domains with different compositions and local structures, i.e. Mg-rich and Co-rich domains, and hydrogen was located only in the Mg-rich domain.

Type
Research Article
Copyright
Copyright © Materials Research Society 2011

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