Phase abundances in AB2 metal hydride alloys and their correlations to various properties

The phase abundances of 16 alloys with various contents of Sn, Co, Al, and Fe additives were studied by Xray diffraction analysis. Due to relative small percentages, the relative abundances of these minor phases were obtained through smoothing, curve fitting, and area integration and correlated qualitatively to the amount of additives in the alloys. In the Laves phases, Sn, Co, and Fe with more outer-shell electrons than that of the host alloy promote C15 phase. Al, with less outer-shell electrons, on the other hand, promotes C14 phase. In the AB phases, Sn promotes the formation of ZrNi phase and suppresses the formation of TiNi phase. In the competition between Zr7Ni10 and Zr9Ni11 (both are the products from a solid-state transformation). Sn promotes Zr7Ni10 while both Fe and Al promote Zr9Ni11. The phase abundances were further correlated to the gas phase and electrochemical properties of the alloys. C14. Zr9Ni11, and TiNi phases were found to increase both the gas phase and electrochemical storage capacities, lower the hydrogen equilibrium pressure, decrease the half-cell high-rate dischargeability, improve both charge retention and cycle life, and slightly decrease the capacity recovery after storing at 45 degrees C for 60 days. C15, ZrNi, and Zr7Ni10 phases work in the opposite manner. (C) 2010 Elsevier B.V. All rights reserved.