Crystal structure and hydrogen absorption of TixZr1−xMn2

TixZr1−xMn2 alloys and their hydrides with x = 0, 0.1, 0.2 and 0.3 were characterized by the XRD Rietveld analysis and isothermal measurement. Introduction of hydrogen did not change the crystal structure type (C14 Laves phase) but led to significant lattice expansion. The best fitting in the Rietveld analysis revealed that titanium atoms preferentially occupied the zirconium sites. Direct comparison of equilibrium pressures of TixZr1−xMn2-H2 system at 269, 298 and 323 K showed that the pressure increased with the titanium content. The absolute values of ΔH and ΔS in α + β two-phase regions monotonously decreased with the titanium content. The variation of ΔS with the titanium content was interpretable by taking into account increased freedom of configuration of hydrogen atoms among various interstitial sites. As for the variation of ΔS with the hydrogen concentration, an unexpected decrease of the absolute value was found for T0.3Zr0.7Mn2-H2 system. We further detected an unusually small size of hydrogen-saturated α phase for T0.3Zr0.7Mn2-H2 system. Those two phenomena would be a symptom of some phase separation on hydriding.