Hydrogen absorption in Ti₄₅Zr_38-xNi_17+x quasicrystals and measurements of the equilibrium vapor pressure

To evaluate their technological usefulness and to probe the local structure of the quasicrystal, p-c-T curves were measured for as-quenched Ti₁₅Zr₃₈Ni₁₇ and Ti₁₅Zr₃₀Ni₂₅ quasicrystal ribbons at 350°C with a computer-controlled apparatus. For both quasicrystals, the p-c-T curves do not exhibit a clear pressure plateau. Instead, the equilibrium vapor pressure remains low (<5 torr) below H/M ≈1; it increases sharply for increasing H/M. Such p-c-T curves may reflect structural features of the quasicrystal. Due to the formation of the crystal hydride phase during the p-c-T measurements, however, the site energy distribution in the quasicrystals could not be obtained. Instead, qualitative conclusions are presented. For Ti₄₅Zr₃₈Ni₁₇ quasicrystals, estimates of the site energy distribution for hydrogen suggest a prominent site located between -0.2 eV and -0.15 eV with a possible broad, weakly binding second peak at higher energy. The site energy locations for hydrogen for Ti₄₅Zr₃₀Ni₂₅ quasicrystals are similar. The Ti₄₅Zr₃₈Ni₁₇ quasicrystals desorb most of the absorbed hydrogen at 650°C in one hour by continuous pumping without phase transformation, and do not become powder after three cycles.