Structural and Hydriding/Dehydriding Properties of HoMn2Hx with Cubic and Hexagonal Laves Phase Structure

Abstract

ABSTRACTBoth the cubic C15-type and the hexagonal C14-type Laves phase compounds HoMn2 were successfully prepared. We found that they absorbed hydrogen up to 3.4 atoms per formula unit at room temperature and discharged it at around 490 K, reversibly. Structural and hydriding/dehydriding properties of the host HoMn2 and their hydrides HoMn2Hx have been investigated by powder X-ray diffraction (XRD) and thermogravimetry/differential thermal analysis (TG/DTA). With increasing the hydrogen content, the host C15-type HoMn2 is distorted into a rhombohedral phase at above x = 2.9, while the host C14-type one keeps the hexagonal structure up to x = 3.4. The experimental results obtained from TG/DTA measurement suggest that two possible interstitial sites with different activation energies for hydrogen desorption exist in the C14 HoMn2, while one site in the C15 HoMn2.