Partial or complete suppression of hysteresis in hydride formation in binary alloys of Pd with other metals

At temperatures below 600 K, the isotherms of hydrogen absorption by Pd exhibit hysteresis loops related to the first-order phase transition or, more specifically, to separation of a diluted phase and hydride. According to the experiments, addition of even small amount of the second metal, e.g. Au or Ta, can appreciably suppress hysteresis. This interesting effect is important in various applications, e.g., in the context of fabrication of efficient hydrogen sensors. To clarify its physical background, we present statistical calculations of the hydrogen absorption isotherms for a series of binary alloys of Pd with Mg, Cu, Ag, Ta, Pt, or Au by using the values of the H-metal interaction provided by the density functional theory (DFT). Aiming at the situations with small amount (<= 15%) of the second metal, the metal atoms in an alloy are considered to be located at random or with short-range correlations. In the random alloy approximation, appreciable suppression of hysteresis is predicted for all the additives under consideration except Cu. Concerning the correlations, we show that the tendency of metals to mixing (as, e.g., predicted for the Pd-Au or Pd-Ta alloy) is in favour of additional suppression of hysteresis whereas the tendency to segregation (as, e.g., predicted for the Pd-Ag alloy) makes the hysteresis loops wider. For Au and Ta, our findings are in good agreement with available experimental data. (c) 2021 The Author(s). Published by Elsevier B.V. CC_BY_4.0