Powder X-ray diffraction under a high-pressure hydrogen atmosphere for Zr–Cr based Laves phase alloys

Abstract

Zr–Cr based Laves phase alloys were investigated by powder X-ray diffraction under a high-pressure hydrogen atmosphere and/or high temperature in order to compare two crystal structures of the same composition. These alloys were synthesized in either the C14 or the C15 type and absorb hydrogen at room temperature. We observed the X-ray diffraction peaks of the C14 type in as-cast ingots and the C15 type in annealed ingots. Line broadening of the X-ray diffraction profile upon hydriding was not observed in either the C14 or C15 phase. The C14 H-free alloys had an axial ratio c/ a slightly smaller than √(8/3), and the C14 hydrides had an axial ratio c/ a slightly larger than √(8/3). Under a high-pressure hydrogen atmosphere, the cell volume of both the C14 and C15 hydrides decreases with an increase in temperature. These phenomena are explained by the change in hydrogen concentration. At constant hydrogen concentration, the cell volume expansion of the C15 phase upon hydrogenation was larger than that of the C14 phase.