Hydrogen absorption characteristics in Zr0.2Ho0.8Fe0.5Co1.5

Hydrogen absorption studies have been carried out on the C15 cubic Laves phase alloy of Zr0.2Ho0.8Fe0.5Co1.5. The p–c data were collected in the pressure and temperature ranges of 0.05 ≤ P (bar) ≤ 45 and 27 ≤ T (°C) ≤ 100, respectively. A maximum hydrogen uptake of 3.6 hydrogen atoms per formula unit at 33 bar and 27°C is observed. The p–c isotherms show one plateau (α + β) region. This is confirmed from the dependence of the thermodynamics of dissolved hydrogen as a function of hydrogen concentration. ΔHH and ΔSH are found to be in the ranges −(5–15) kJ (mol H)−1 and −(23–48) J K−1 (mol H)−1, respectively. Volume expansion of about 20% is found at the maximum hydrogen concentration at RT, without a change in its crystal structure.