FROM PARTITION-FUNCTION TO PHASE-DIAGRAM - STATISTICAL THERMODYNAMICSOF THE LANI5-H SYSTEM

The 6m sites of the LaNi5 lattice are not fully occupied by hydrogen a t moderate pressures due to a blocking effect of the very closely spac ed sites. It is usually not possible to treat this effect rigorously i n continuous lattices. In this case, however, the 6m sites form isolat ed hexagons, for which a partition function can be constructed. The ca lculated absorption isotherms and the phase diagram display the observ ed features of a wide plateau region, which splits into two narrow pla teaus above 338 K, and an additional plateau at pressures above 1000 b ar.