• Nakamura, Yumiko
• Yamazaki, Saishun
• Proffen, Thomas
• Kim, Hyunjeong
• Akiba, Etsuo

Abstract

<jats:title>ABSTRACT</jats:title><jats:p>Crystal and local structures and hydrogen occupation of Mg containing materials, (Mg,Ca)Ni<jats:italic><jats:sub>x</jats:sub></jats:italic> (<jats:italic>x</jats:italic> = 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.</jats:p><jats:p>A C15 Laves phase (Mg<jats:sub>0.67</jats:sub>Ca<jats:sub>0.33</jats:sub>)Ni<jats:sub>2</jats:sub> showed isotropic lattice expansion upon hydrogenation. Mg and Ca occupied the same site randomly. It has two hydrogen sites, Mg(Ca)<jats:sub>2</jats:sub>Ni<jats:sub>2</jats:sub> site and M(Ca)Ni<jats:sub>3</jats:sub> site.</jats:p><jats:p>Mg<jats:sub>2</jats:sub>CaNi<jats:sub>9</jats:sub>, MgCa<jats:sub>2</jats:sub>Ni<jats:sub>9</jats:sub>, and CaNi<jats:sub>3</jats:sub> compounds consisted of MgZn<jats:sub>2</jats:sub>-type (Mg,Ca)<jats:sub>2</jats:sub>Ni<jats:sub>4</jats:sub> cell and CaCu<jats:sub>5</jats:sub>-type CaNi<jats:sub>5</jats:sub> cell stacking along the <jats:italic>c</jats:italic>-axis. The MgZn<jats:sub>2</jats:sub>-type cell was occupied by only Mg in Mg<jats:sub>2</jats:sub>CaNi<jats:sub>9</jats:sub>, and randomly occupied by both Mg and Ca in MgCa<jats:sub>2</jats:sub>Ni<jats:sub>9</jats:sub>. Expansion of this cell strongly depended on the composition: larger expansion was observed in a Ca-rich composition.</jats:p><jats:p>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.</jats:p>

Topics

• compound
• phase
• Hydrogen
• neutron diffraction
• isotropic
• intermetallic