On the "imaginary binary hydrides" model

The "imaginary binary hydrides" (IBH) model has been elaborated to predict the relative hydrogen site occupation in intermetallic hydrides. Utilization of Miedema's first version for calculating heats of formation ΔH of binary hydrides for input into the IBH model has led to good quantitative agreement with some experimentally derived data. Application of later versions for calculating ΔH values of binary hydrides for input into the IBH model yield unsatisfactory quantitative predictions. In the present work an attempt is made to understand the reason for the significant difference in the results of the IBH model upon the application of the various schemes for calculating ΔH values of binary hydrides. Consequently, several available experimental results for the heats of formation of metal-hydrogen systems in their solubility regions are considered. At high hydrogen concentrations the later versions, mentioned above, yield improved estimations of ΔH values. At low hydrogen compositions, however, Miedema's original model better reflects the variational behaviour of ΔH, especially in view of the fact that a constant term in ΔH does not change the results of the IBH procedure.