A method based upon isothermal measurements of p(n) and χ(n) (where p was the pressure of D2 or H2, n was the atomic ratio D:Pd or H:Pd and χ was the magnetic susceptibility) was applied to the field about the critical point. Evaluation of the p(n) isotherms measured in the homogeneous solution phase above the critical temperature, Tc, yielded a value of the critical concentration, nc = 0.257, for Pd-D2 and Pd-H2. On the basis of this nc value, the other critical data were re-determined. The values of Tc = 556K and pc = 39bar, obtained for Pd-D2 deviated markedly from those previously accepted. By means of the absorption and desorption branches of the p(n) and χ(n) isotherms, measured across the two-phase region below Tc, the boundaries of this region (coexistence curve) could be determined. Different boundary lines for absorption and desorption were obtained in the T vs n diagram, resulting in nc(abs) = 0.295 and nc(des) = 0.255; which were also equal for both isotopes. The shift of the coexistence curve obtained from the absorption measurements, relative to that resulting from desorption, was interpreted as being a consequence of the constraining pressure effect upon the more voluminous β-phase. By means of this shift, the hysteretic behaviour of the χ(n) isotherms also became understandable.

New Experiments on and Interpretations of Hysteresis Effects of Pd-D2 and Pd-H2. E.Wicke, J.Blaurock: Journal of the Less Common Metals, 1987, 130, 351-63