Proposal for new indexes describing the degree of hysteresis and those applications to the ZrMn2-H2 systems

For purposes of comparing the degrees of hysteresis between different alloy-hydrogen systems, three kinds of indexes have been proposed instead of the conventional hysteresis factors. The new indexes are defined in the P-T-diagram by the thermodynamic parameters being independent of measurement temperature. Each index has shown that the degrees of hysteresis for the ZrMn2-H-2 systems increases with decreasing lattice constants. A literature review has made it clear that the hydrogen-induced volume expansion for the ZrMn2-based alloys increases with decreasing lattice constants. These four relationships could be described in terms of hyperbolic regression expressions. Delta S/Delta H shows close hyperbolic relationships with the lattice constants both for hydrogen absorption and for desorption. (C) 1998 Elsevier Science S.A. All rights reserved.