HEAT-CAPACITY ASSOCIATED WITH HYDROGEN ORDERING IN SUPERSTOICHIOMETRIC RARE-EARTH DIHYDRIDES - THE CASE OF LAH2-LIKE SYSTEMS(X)

In the case of beta-RH(2+x) systems (R--rare earth; 0 < x < 1), the fr action I of the hydrogen atoms located in the octahedral interstitial sites of the f.c.c. metal lattice undergoes order-disorder and order-o rder transformations. The strength of these transformations and the po ssibility of their experimental observation in the investigation of th e thermal properties of metal-hydrogen compounds can be estimated by c alculating the temperature dependence of the internal energy, (E) over bar(T), and of the specific heat, C(T) = partial derivative (E) over bar(T)/partial derivative T. The calculation is applied for the case o f the LaH2+x-like systems, with different concentrations x and differe nt energy-parameter ratios p equivalent to V-2/V-1. Copyright (C) 1996 Elsevier Science Ltd